Waveguides having integrated spacers, waveguides having edge absorbers, and methods for making the same

ABSTRACT

In some embodiments, a head-mounted, near-eye display system comprises a stack of waveguides having integral spacers separating the waveguides. The waveguides may each include diffractive optical elements that are formed simultaneously with the spacers by imprinting. The spacers are disposed on one major surface of each of the waveguides and indentations are provided on an opposite major surface of each of the waveguides. The indentations are sized and positioned to align with the spacers, thereby forming a self-aligned stack of waveguides. Tops of the spacers may be provided with light scattering features, anti-reflective coatings, and/or light absorbing adhesive to prevent light leakage between the waveguides. As seen in a top-down view, the spacers may be elongated along the same axis as the diffractive optical elements. The waveguides may include structures (e.g., layers of light absorbing materials, rough surfaces, light out-coupling optical elements, and/or light trapping microstructures) along their edges to mitigate reflections and improve the display contrast.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a US National Phase application filed under 35U.S.C. § 371 of PCT/US2019/025236, which claims priority to U.S. PatentProv. App. 62/651,502, which is titled “WAVEGUIDES HAVING INTEGRATEDSPACERS AND METHODS FOR MAKING THE SAME” and was filed on Apr. 2, 2018.The above-recited application is incorporated herein by reference in itsentirety.

This application incorporates by reference the entirety of each of thefollowing patent applications: U.S. application Ser. No. 14/555,585filed on Nov. 27, 2014, published on Jul. 23, 2015 as U.S. PublicationNo. 2015/0205126; U.S. application Ser. No. 14/690,401 filed on Apr. 18,2015, published on Oct. 22, 2015 as U.S. Publication No. 2015/0302652;U.S. application Ser. No. 14/212,961 filed on Mar. 14, 2014, now U.S.Pat. No. 9,417,452 issued on Aug. 16, 2016; U.S. application Ser. No.14/331,218 filed on Jul. 14, 2014, published on Oct. 29, 2015 as U.S.Publication No. 2015/0309263; and U.S. Application No. 62/651,507 filedon Apr. 2, 2018, entitled HYBRID POLYMER WAVEGUIDE AND METHODS FORMAKING THE SAME.

BACKGROUND Field

The present disclosure relates to display systems and, moreparticularly, to augmented reality display systems.

Description of the Related Art

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” or “augmentedreality” experiences, wherein digitally reproduced images or portionsthereof are presented to a user in a manner wherein they seem to be, ormay be perceived as, real. A virtual reality, or “VR”, scenariotypically involves presentation of digital or virtual image informationwithout transparency to other actual real-world visual input; anaugmented reality, or “AR”, scenario typically involves presentation ofdigital or virtual image information as an augmentation to visualizationof the actual world around the user. A mixed reality, or “MR”, scenariois a type of AR scenario and typically involves virtual objects that areintegrated into, and responsive to, the natural world. For example, inan MR scenario, AR image content may be blocked by or otherwise beperceived as interacting with objects in the real world.

Referring to FIG. 1, an augmented reality scene 10 is depicted wherein auser of an AR technology sees a real-world park-like setting 20featuring people, trees, buildings in the background, and a concreteplatform 30. In addition to these items, the user of the AR technologyalso perceives that he “sees” “virtual content” such as a robot statue40 standing upon the real-world platform 30, and a cartoon-like avatarcharacter 50 flying by which seems to be a personification of a bumblebee, even though these elements 40, 50 do not exist in the real world.Because the human visual perception system is complex, it is challengingto produce an AR technology that facilitates a comfortable,natural-feeling, rich presentation of virtual image elements amongstother virtual or real-world imagery elements.

Systems and methods disclosed herein address various challenges relatedto AR and VR technology.

SUMMARY

In some embodiments, a display system comprises an eyepiece comprising astack of waveguides. At least one of the waveguides comprises anoptically transmissive body. The optically transmissive body comprises:diffractive optical elements comprising a plurality of protrusions andintervening recesses on a major surface of the optically transmissivebody; and a plurality of spacers integral with the opticallytransmissive body. The spacers extend to a height greater than a heightof the diffractive optical elements, and the overlying waveguide isdisposed on the spacers. The spacers separate the optically transmissivebody from the overlying waveguide by a gap.

In some other embodiments, a display system comprises an eyepiececomprising a waveguide. The waveguide comprises an opticallytransmissive body. The optically transmissive body comprises diffractiveoptical elements comprising: a plurality of protrusions and interveningrecesses on a major surface of the optically transmissive body; and aplurality of spacers integral with the optically transmissive body. Thespacers extend from the major surface to a height greater than a heightof the diffractive optical elements.

In yet other embodiments, a method for making an eyepiece is provided.The method comprises forming a waveguide. Forming the waveguidecomprises defining integral diffractive optical elements and integralspacers on a major surface of the waveguide. The spacers arespaced-apart from the diffractive optical elements and extend to aheight above the diffractive optical elements.

In addition, various examples of embodiments are provided below.

Example 1: A display system comprising:

-   -   an eyepiece comprising a stack of waveguides, wherein at least        one of the waveguides comprises:        -   an optically transmissive body comprising:            -   diffractive optical elements comprising a plurality of                protrusions and intervening recesses on a major surface                of the optically transmissive body; and            -   a plurality of spacers integral with the optically                transmissive body,                -   wherein the spacers extend to a height greater than                    a height of the diffractive optical elements,                -   wherein the overlying waveguide is disposed on the                    spacers, and                -   wherein the spacers separate the optically                    transmissive body from the overlying waveguide by a                    gap.

Example 2: The display system of Example 1, wherein the overlyingwaveguide comprises indentations accommodating the spacers in theindentations.

Example 3: The display system of Example 2, wherein each of thewaveguides comprises spacers and indentations, wherein the indentationsaccommodate spacers of underlying waveguides.

Example 4: The display system of any of Examples 2 to 3, wherein thespacers comprise multiple tiers having progressively narrower widthswith increasing height, wherein the indentations comprise openingshaving multiple tiers with narrower widths as height increases.

Example 5: The display system of any of Examples 1 to 4, wherein sizesof the spacers varies across the major surface.

Example 6: The display system of any of Examples 1 to 5, wherein thespacers are arranged in groups, wherein neighboring spacers of a grouphave different sizes.

Example 7: The display system of any of Examples 1 to 6, wherein, asseen in a top-down view, the spacers comprise one or more shapesselected from the group consisting of rectangular prism, rectangularpyramid, triangular prism, triangular pyramid, cylinder, and cone.

Example 8: The display system of any of the Examples 1 to 7, furthercomprising an adhesive attaching the spacers to the overlying waveguide.

Example 9: The display system of Example 8, wherein the adhesive isconfigured to absorb light.

Example 10: The display system of any of the Examples 1 to 9, furthercomprising a pattern of light scattering features on tops of thespacers.

Example 11: The display system of any of the Examples 1 to 10, whereinthe overlying waveguide comprises diffractive optical elementsconfigured to redirect light of different wavelengths than thediffractive optical elements of the at least one of the waveguides.

Example 12: The display system of any of the Examples 1 to 11, whereinthe gap is an air gap.

Example 13: A display system comprising:

-   -   an eyepiece comprising a waveguide comprising:        -   an optically transmissive body comprising:            -   diffractive optical elements comprising a plurality of                protrusions and intervening recesses on a major surface                of the optically transmissive body, and            -   a plurality of spacers integral with the optically                transmissive body, wherein the spacers extend from the                major surface to a height greater than a height of the                diffractive optical elements.

Example 14: A method for making an eyepiece, the method comprising:

-   -   forming a waveguide, wherein forming the waveguide comprises:        -   defining integral diffractive optical elements and integral            spacers on a major surface of the waveguide, where the            spacers are spaced-apart from the diffractive optical            elements and extend to a height above the diffractive            optical elements.

Example 15: The method of Example 14, wherein the diffractive opticalelements and the spacers are formed simultaneously.

Example 16: The method of any of the Examples 14 to 15, wherein definingintegral diffractive optical element and integral spacers comprisespatterning light scattering features on tops of the spacers.

Example 17: The method of any of the Examples 14 to 16, wherein definingintegral diffractive optical elements and integral spacers comprises:

-   -   providing upper and lower imprint molds, wherein the imprint        molds face one another;    -   providing a flowable material on the lower imprint mold;    -   contacting the flowable material with the upper imprint mold;    -   exposing the flowable material to a hardening process, wherein        the hardened flowable material forms the waveguide; and    -   removing the upper and lower imprint molds.

Example 18: The method of Example 17, wherein the upper imprint moldcomprises a pattern of protrusions and indentations, wherein contactingthe flowable material with the upper imprint mold transfers acorresponding pattern of protrusions and indentations into the flowablematerial to imprint the diffractive optical elements and spacers in theflowable material.

Example 19: The method of Example 17, further comprising, after exposingthe flowable material to the hardening process:

-   -   removing the upper imprint mold;    -   depositing an other flowable material on the hardened flowable        material; and    -   contacting the other flowable material with an other upper        imprint mold, wherein the other upper imprint mold comprises a        pattern of protrusions and indentations, wherein contacting the        flowable material with the upper imprint mold transfers a        corresponding pattern of protrusions and indentations into the        flowable material to imprint the diffractive optical elements        and spacers in the flowable material

Example 20: The method of any of the Examples 14 to 19, wherein, as seenin a top-down view, the diffractive optical elements comprise adiffractive grating comprising a plurality of protrusions elongatedalong an axis, wherein the spacers are elongated and have a lengthextending along the axis.

Example 21: The method of Example 20, wherein the spacers are arrayedalong a plurality of sides of the waveguide, wherein spacers on each ofthe plurality of sides are elongated and have lengths extending alongthe axis.

Example 22: The method of Example 17, wherein the lower imprint moldcomprises a pattern of protrusions and indentations, wherein providingthe flowable material on the lower imprint mold forms a correspondingpattern of protrusions and indentations in the flowable material.

Example 23: The method of Example 22, wherein the corresponding patternof protrusions and indentations forming diffractive optical elements andindentations are positioned and sized to receive spacers into theindentations.

Example 24: The method of any of the Examples 17 to 23, wherein exposingthe flowable material to a hardening process comprises exposing theflowable material to ultraviolet light.

Example 25: The method of any of the Examples 14 to 24, furthercomprising stacking an other waveguide on the spacers, wherein thespacers support the other waveguide and define a gap between thewaveguide and the other waveguide.

Example 26: The method of Example 25, wherein the other waveguidecomprises diffractive optical elements configured to redirect light ofdifferent wavelengths from the diffractive optical elements of thewaveguide.

Example 27: The method of any of the Examples 14 to 26, wherein definingintegral diffractive optical elements and integral spacers comprisessimultaneously defining in coupling optical elements, orthogonal pupilexpanders, and exit pupil expanders.

Example 28: The method of any of the Examples 14 to 27, wherein theflowable material is a polymer material.

Example 29: A display system comprising:

-   -   an eyepiece comprising a waveguide configured to propagate light        therein by total internal reflection, the waveguide having top        and bottom major surfaces and an edge therebetween, wherein the        waveguide is formed of an optically transmissive material; and    -   light absorbing material disposed on and contacting the edge of        the waveguide, wherein a difference in refractive index between        the optically transmissive material forming the waveguide and        the light absorbing material is less than 0.2.

Example 30: The display system of Example 29, wherein an extinctioncoefficient of the light absorbing material is greater than 0.02.

Example 31: The display system of any of the Examples 29 to 30, whereinthe light absorbing material extends out at least 2 mm from the edge ofthe waveguide to cover portions of the top and bottom major surfacesadjacent the edge.

Example 32: The display system of any of the Examples 29 to 31, whereinthe light absorbing material extends out 2-5 mm from the edge of thewaveguide.

Example 33: The display system of any of the Examples 29 to 32, whereinthe light absorbing material is at least 20 micrometers thick.

Example 34: The display system of any of the Examples 29 to 33, whereinthe light absorbing material comprises one or more of a Fullerene,graphene, amorphous silicon, and germanium.

Example 35: The display system of any of the Examples 29 to 34, whereinthe light absorbing material comprises a blank ink.

Example 36: The display system of any of the Examples 29 to 35, whereinthe light absorbing material comprises a polymer having one or moreadditives dispersed therein.

Example 37: The display system of Example 36, wherein the additivecomprises one or more of carbon black, carbon nanopowder, carbonnanotubes, metallic nanoparticles, color dye, pigment, and phosphor.

Example 38: The display system of Example 36, wherein the additive is acarbon nanopowder having a concentration of at least 0.4% carbonnanopowder.

Example 39: The display system of Example 38, wherein the concentrationis 0.4 to 1.56%.

Example 40: The display system of any of the Examples 29 to 39, whereinthe waveguide is part of a stack of waveguides, wherein the waveguidecomprises an integral spacer separating the waveguide from animmediately neighboring waveguide.

Example 41: A display system comprising:

-   -   an eyepiece comprising a waveguide having top and bottom major        surfaces and an edge extending between the top and bottom major        surfaces, wherein the waveguide is configured to propagate light        between the top and bottom major surfaces by total internal        reflection,    -   wherein the edge has a rough texture,    -   wherein, within 2 mm of the edge, at least one of the top and        bottom major surfaces has a rough texture, and    -   wherein the rough textures of edge and the at least one of the        top and bottom major surfaces form a rougher surface than        portions of the top and bottom major surfaces configured to        provide total internal reflection therebetween.

Example 42: The display system of Example 41, wherein the rough texturesof both the top and bottom major surfaces extend out 2-5 mm from theedge.

Example 43: The display system of any of the Examples 41 to 42, whereinthe rough textures of the top and bottom major surfaces and the edgehave a same roughness level.

Example 44: The display system of any of the Examples 41 to 43, whereinthe rough textures of the top and bottom major surfaces and the edgehave a surface roughness (Sa) of 1-100.

Example 45: The display system of any of the Examples 41 to 44, furthercomprising a light absorbing material disposed on and covering the edgeand the portions of the top and bottom major surfaces having the roughtexture.

Example 46: The display system of Example 45, wherein the lightabsorbing material covers an area 2-5 mm beyond the portions of the topand bottom major surfaces having the rough textures.

Example 47: The display system of any of the Examples 45 to 46, whereina difference in refractive index between material forming the waveguideand the light absorbing material is less than 0.2.

Example 48: The display system of any of the Examples 41 to 47, whereinthe waveguide is part of a stack of waveguides, wherein the waveguidecomprises an integral spacer separating the waveguide from animmediately neighboring waveguide.

Example 49: A display system comprising:

-   -   an eyepiece comprising a waveguide having top and bottom major        surfaces and an edge extending between the top and bottom major        surfaces, wherein the waveguide is configured to propagate light        between the top and bottom major surfaces by total internal        reflection,    -   wherein the waveguide comprises one or more of light        out-coupling optical elements and light trapping microstructures        along the edge.

Example 50: The display system of Example 49, wherein the lightout-coupling optical elements are diffractive gratings.

Example 51: The display system of any of the Examples 49 to 50, whereinthe one or more of light out-coupling optical elements and lighttrapping microstructures extend out, on one or both of the top andbottom major surfaces, by 2-5 mm from the edge.

Example 52: The display system of any of the Examples 49 to 51, furthercomprising a light absorbing material disposed on and covering the edgeand the one or more of light out-coupling optical elements and lighttrapping microstructures.

Example 53: The display system of any of the Examples 49 to 52, whereinthe light absorbing material covers an area 2-5 mm beyond portions ofthe top and bottom major surfaces having the one or more of lightout-coupling optical elements and light trapping microstructures.

Example 54: The display system of any of the Examples 49 to 53, whereinthe waveguide is part of a stack of waveguides, wherein the waveguidecomprises an integral spacer separating the waveguide from animmediately neighboring waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user's view of augmented reality (AR) through an ARdevice.

FIG. 2 illustrates a conventional display system for simulatingthree-dimensional imagery for a user.

FIGS. 3A-3C illustrate relationships between radius of curvature andfocal radius.

FIG. 4A illustrates a representation of the accommodation-vergenceresponse of the human visual system.

FIG. 4B illustrates examples of different accommodative states andvergence states of a pair of eyes of the user.

FIG. 4C illustrates an example of a representation of a top-down view ofa user viewing content via a display system.

FIG. 4D illustrates another example of a representation of a top-downview of a user viewing content via a display system.

FIG. 5 illustrates aspects of an approach for simulatingthree-dimensional imagery by modifying wavefront divergence.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user.

FIG. 7 illustrates an example of exit beams outputted by a waveguide.

FIG. 8 illustrates an example of a stacked waveguide assembly in whicheach depth plane includes images formed using multiple differentcomponent colors.

FIG. 9A illustrates a cross-sectional side view of an example of a setof stacked waveguides that each includes an in coupling optical element.

FIG. 9B illustrates a perspective view of an example of the plurality ofstacked waveguides of FIG. 9A.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B.

FIG. 9D illustrates an example of wearable display system.

FIG. 10A illustrates an example of a waveguide comprising spacers.

FIG. 10B illustrates examples of 3-dimensional shapes for spacers andindentations for accommodating the spacers.

FIG. 10C illustrates an example of a stack of waveguides comprisingspacers.

FIG. 11A illustrates an example of a waveguide comprising spacers withlight scattering features.

FIG. 11B illustrates an example of a stack of waveguides comprisingspacers and light leakage prevention material at the interface betweenspacers and immediately neighboring waveguides.

FIGS. 12A-12C illustrate an example of a method for forming a waveguidewith spacers.

FIGS. 13A-13B illustrate examples of top-down plan views of waveguidescomprising spacers.

FIG. 14 illustrates an example of a waveguide comprising spacers andindentations of varying dimensions.

FIGS. 15A-15G illustrate an example of a method for forming a hybridwaveguide with spacers.

FIG. 16 illustrates an example of a waveguide having edges covered withabsorbing material.

FIGS. 17-18 illustrate an example of a waveguide having light absorbingmaterial extending on portions of top and bottom major surfaces of thewaveguide.

FIGS. 19-20 illustrate simulation results of light absorption as afunction of incident angle for different absorbing materials.

FIG. 21 illustrates an example of a waveguide having roughened edges,which may be covered with absorbing materials.

FIG. 22A illustrates an example of a waveguide having edges without-coupling gratings and absorbing materials.

FIGS. 22B-22C illustrates an example of a waveguide having edges withlight trapping structures and light absorbing materials.

FIG. 23 illustrates edges of examples of the placement of lightabsorbing materials along edges of a waveguide.

FIG. 24 illustrates a stack of waveguides with integral spacers.

DETAILED DESCRIPTION

Near-eye augmented and virtual reality display systems may includeeyepieces for directing image information into the eyes of a viewer. Theeyepieces may be formed of stacks of waveguides that are spaced apart byintervening beads of glue. It will be appreciated that the sizes of thebeads and the separation between the waveguides provided by the beadsmay impact the optical performance of the eyepiece and the perceivedimage quality of the display system. For example, the beads may beformed at specific locations and then an overlying waveguide may bepressed onto the beads at specific pressures, after which the beads maybe hardened by curing. As a result, formation of the spacers may requireprecise alignment and controlled pressure to maintain a constantseparation distance between the waveguides throughout the stack ofwaveguides. It may be challenging to provide such precise alignment andpressure control. In addition, where the waveguides are formed ofpolymers, the polymer waveguides may be flexible and utilizing beads ofmaterial to separate the waveguides may not provide sufficientmechanical or structural stability for maintaining the desiredseparation between waveguides.

In some embodiments, one or more waveguides, which may be used to form astack of waveguides, may include integral spacers for providing adesired separation with overlying or underlying structures, such asother waveguides. The waveguides may each include surface relieffeatures, e.g. diffractive optical elements that are formedsimultaneously with the spacer, such as by imprinting. In someembodiments, the spacers and the main body of the waveguides form amonolithic structure. In some embodiments, the waveguide may be a hybridwaveguide comprising a plurality of layers, one of which may include thespacers and the diffractive optical elements. In some embodiments, thespacers may be laterally elongated along the same axis as thediffractive optical elements, which may facilitate the fabrication ofthe spacers and diffractive optical elements without deforming thesefeatures.

In some embodiments, the spacers and/or indentations may have varyingsizes, e.g., widths, and/or multiple spacers and/or indentations may beformed as neighboring groups of spacers and/or indentations. Forexample, both major surfaces of the waveguide may include spacers andindentations, thereby forming an interlocking system of spacers andindentations with underlying and/or overlying matching waveguides.Advantageously, the varying sizes and/or neighboring groups of spacersand/or indentations may increase the mechanical and structural stabilityof a single waveguide and/or stack of waveguides.

In some embodiments, the spacers are disposed on one major surface of awaveguide and indentations are provided on an opposite major surface ofthe waveguide. The indentations are sized and positioned to align withspacers of immediately neighboring waveguides, thereby forming aself-aligned stack of waveguides. Tops of the spacers may be providedwith light scattering features and/or a light leakage preventionmaterial (e.g., an anti-reflective coating and/or a light absorbingmaterial) to prevent light leakage between the waveguides.

In some embodiments, different waveguides of the stack of waveguides maybe configured to incouple and/or outcouple light of different colors,e.g., different component colors for forming a full-color image. Inaddition or alternatively, different waveguides of the waveguides may beconfigured to output light with different amounts of wavefrontdivergence, to display image content at different apparent distancesfrom the viewer.

Advantageously, the spacers integral with the waveguides provide a rigidstructure for easily and reproducibility separating spacers of a stackof spacers. In addition, providing matching indentations in thewaveguides further facilitates the making of consistent stacks ofspacers by providing self-aligned stacking. The consistent separationbetween spacers may provide consistent optical performance byconsistently preventing light from leaking between the waveguides, inaddition to facilitating the total internal reflection of light throughindividual waveguides. Moreover, manufacturing processes may besimplified by eliminating separate steps for depositing beads of thematerial, precisely applying pressure to waveguides, and then hardeningthe glue material. Rather, where the waveguides comprise diffractiveoptical elements, the spacers may be formed simultaneously with thediffractive optical elements.

As discussed herein, waveguides may form eyepieces for augmented andvirtual reality display systems. The waveguides may be configured tooutput light to display image content for a viewer. It will appreciatedthat some light beams within the waveguides may travel through thewaveguides without being outcoupled for the viewer. Such light may bereferred to herein as unutilized light. Unutilized light may, in somecircumstances, reflect off of edges of the waveguides and propagate backthrough the waveguides, where the light may propagate out of thewaveguide (e.g. be out-coupled by outcoupling elements in thewaveguides, or escape total internal reflection due to the angles atwhich the light reflects off of the edges). Undesirably, thispropagation of unutilized light out of the waveguide may cause visualartifacts such as ghosting and/or reductions in the contrast of thedisplay system.

In some embodiments, one or more waveguides, which may be used to form astack of waveguides (which may include integral spacers to separateneighboring waveguides), may include edge treatments to reduce ormitigate unwanted reflections and propagation of unutilized light out ofa waveguide, thus improving image quality. The edge treatments mayinclude, as examples, light absorbing material that is applied to one ormore edges of the waveguide and/or reflection-preventing structuresformed at those edges. In some embodiments, the edge treatments mayinclude blackening materials, black ink, light absorbing materials, edgeroughening, out-coupling gratings, light-trapping structures, absorbingpolymers, and combinations of these and other treatments.

Advantageously, in some embodiments, various edge treatments may beformed simultaneously with the formation of spacers and/or diffractiveoptical elements. For example, an imprint mold may include patterns fordefining the edge treatments (e.g., the patterns may define a roughtexture, out-coupling optical elements, and/or light trappingmicrostructures).

Reference will now be made to the drawings, in which like referencenumerals refer to like parts throughout. Unless indicated otherwise, thedrawings are schematic not necessarily drawn to scale.

Example Display Systems

FIG. 2 illustrates a conventional display system for simulatingthree-dimensional imagery for a user. It will be appreciated that auser's eyes are spaced apart and that, when looking at a real object inspace, each eye will have a slightly different view of the object andmay form an image of the object at different locations on the retina ofeach eye. This may be referred to as binocular disparity and may beutilized by the human visual system to provide a perception of depth.Conventional display systems simulate binocular disparity by presentingtwo distinct images 190, 200 with slightly different views of the samevirtual object—one for each eye 210, 220—corresponding to the views ofthe virtual object that would be seen by each eye were the virtualobject a real object at a desired depth. These images provide binocularcues that the user's visual system may interpret to derive a perceptionof depth.

With continued reference to FIG. 2, the images 190, 200 are spaced fromthe eyes 210, 220 by a distance 230 on a z-axis. The z-axis is parallelto the optical axis of the viewer with their eyes fixated on an objectat optical infinity directly ahead of the viewer. The images 190, 200are flat and at a fixed distance from the eyes 210, 220. Based on theslightly different views of a virtual object in the images presented tothe eyes 210, 220, respectively, the eyes may naturally rotate such thatan image of the object falls on corresponding points on the retinas ofeach of the eyes, to maintain single binocular vision. This rotation maycause the lines of sight of each of the eyes 210, 220 to converge onto apoint in space at which the virtual object is perceived to be present.As a result, providing three-dimensional imagery conventionally involvesproviding binocular cues that may manipulate the vergence of the user'seyes 210, 220, and that the human visual system interprets to provide aperception of depth.

Generating a realistic and comfortable perception of depth ischallenging, however. It will be appreciated that light from objects atdifferent distances from the eyes have wavefronts with different amountsof divergence. FIGS. 3A-3C illustrate relationships between distance andthe divergence of light rays. The distance between the object and theeye 210 is represented by, in order of decreasing distance, R1, R2, andR3. As shown in FIGS. 3A-3C, the light rays become more divergent asdistance to the object decreases. Conversely, as distance increases, thelight rays become more collimated. Stated another way, it may be saidthat the light field produced by a point (the object or a part of theobject) has a spherical wavefront curvature, which is a function of howfar away the point is from the eye of the user. The curvature increaseswith decreasing distance between the object and the eye 210. While onlya single eye 210 is illustrated for clarity of illustration in FIGS.3A-3C and other figures herein, the discussions regarding eye 210 may beapplied to both eyes 210 and 220 of a viewer.

With continued reference to FIGS. 3A-3C, light from an object that theviewer's eyes are fixated on may have different degrees of wavefrontdivergence. Due to the different amounts of wavefront divergence, thelight may be focused differently by the lens of the eye, which in turnmay require the lens to assume different shapes to form a focused imageon the retina of the eye. Where a focused image is not formed on theretina, the resulting retinal blur acts as a cue to accommodation thatcauses a change in the shape of the lens of the eye until a focusedimage is formed on the retina. For example, the cue to accommodation maytrigger the ciliary muscles surrounding the lens of the eye to relax orcontract, thereby modulating the force applied to the suspensoryligaments holding the lens, thus causing the shape of the lens of theeye to change until retinal blur of an object of fixation is eliminatedor minimized, thereby forming a focused image of the object of fixationon the retina (e.g., fovea) of the eye. The process by which the lens ofthe eye changes shape may be referred to as accommodation, and the shapeof the lens of the eye required to form a focused image of the object offixation on the retina (e.g., fovea) of the eye may be referred to as anaccommodative state.

With reference now to FIG. 4A, a representation of theaccommodation-vergence response of the human visual system isillustrated. The movement of the eyes to fixate on an object causes theeyes to receive light from the object, with the light forming an imageon each of the retinas of the eyes. The presence of retinal blur in theimage formed on the retina may provide a cue to accommodation, and therelative locations of the image on the retinas may provide a cue tovergence. The cue to accommodation causes accommodation to occur,resulting in the lenses of the eyes each assuming a particularaccommodative state that forms a focused image of the object on theretina (e.g., fovea) of the eye. On the other hand, the cue to vergencecauses vergence movements (rotation of the eyes) to occur such that theimages formed on each retina of each eye are at corresponding retinalpoints that maintain single binocular vision. In these positions, theeyes may be said to have assumed a particular vergence state. Withcontinued reference to FIG. 4A, accommodation may be understood to bethe process by which the eye achieves a particular accommodative state,and vergence may be understood to be the process by which the eyeachieves a particular vergence state. As indicated in FIG. 4A, theaccommodative and vergence states of the eyes may change if the userfixates on another object. For example, the accommodated state maychange if the user fixates on a new object at a different depth on thez-axis.

Without being limited by theory, it is believed that viewers of anobject may perceive the object as being “three-dimensional” due to acombination of vergence and accommodation. As noted above, vergencemovements (e.g., rotation of the eyes so that the pupils move toward oraway from each other to converge the lines of sight of the eyes tofixate upon an object) of the two eyes relative to each other areclosely associated with accommodation of the lenses of the eyes. Undernormal conditions, changing the shapes of the lenses of the eyes tochange focus from one object to another object at a different distancewill automatically cause a matching change in vergence to the samedistance, under a relationship known as the “accommodation-vergencereflex.” Likewise, a change in vergence will trigger a matching changein lens shape under normal conditions.

With reference now to FIG. 4B, examples of different accommodative andvergence states of the eyes are illustrated. The pair of eyes 222 a isfixated on an object at optical infinity, while the pair eyes 222 b arefixated on an object 221 at less than optical infinity. Notably, thevergence states of each pair of eyes is different, with the pair of eyes222 a directed straight ahead, while the pair of eyes 222 converge onthe object 221. The accommodative states of the eyes forming each pairof eyes 222 a and 222 b are also different, as represented by thedifferent shapes of the lenses 210 a, 220 a.

Undesirably, many users of conventional “3-D” display systems find suchconventional systems to be uncomfortable or may not perceive a sense ofdepth at all due to a mismatch between accommodative and vergence statesin these displays. As noted above, many stereoscopic or “3-D” displaysystems display a scene by providing slightly different images to eacheye. Such systems are uncomfortable for many viewers, since they, amongother things, simply provide different presentations of a scene andcause changes in the vergence states of the eyes, but without acorresponding change in the accommodative states of those eyes. Rather,the images are shown by a display at a fixed distance from the eyes,such that the eyes view all the image information at a singleaccommodative state. Such an arrangement works against the“accommodation-vergence reflex” by causing changes in the vergence statewithout a matching change in the accommodative state. This mismatch isbelieved to cause viewer discomfort. Display systems that provide abetter match between accommodation and vergence may form more realisticand comfortable simulations of three-dimensional imagery.

Without being limited by theory, it is believed that the human eyetypically may interpret a finite number of depth planes to provide depthperception. Consequently, a highly believable simulation of perceiveddepth may be achieved by providing, to the eye, different presentationsof an image corresponding to each of these limited numbers of depthplanes. In some embodiments, the different presentations may provideboth cues to vergence and matching cues to accommodation, therebyproviding physiologically correct accommodation-vergence matching.

With continued reference to FIG. 4B, two depth planes 240, correspondingto different distances in space from the eyes 210, 220, are illustrated.For a given depth plane 240, vergence cues may be provided by thedisplaying of images of appropriately different perspectives for eacheye 210, 220. In addition, for a given depth plane 240, light formingthe images provided to each eye 210, 220 may have a wavefront divergencecorresponding to a light field produced by a point at the distance ofthat depth plane 240.

In the illustrated embodiment, the distance, along the z-axis, of thedepth plane 240 containing the point 221 is 1 m. As used herein,distances or depths along the z-axis may be measured with a zero-pointlocated at the exit pupils of the user's eyes. Thus, a depth plane 240located at a depth of 1 m corresponds to a distance of 1 m away from theexit pupils of the user's eyes, on the optical axis of those eyes withthe eyes directed towards optical infinity. As an approximation, thedepth or distance along the z-axis may be measured from the display infront of the user's eyes (e.g., from the surface of a waveguide), plus avalue for the distance between the device and the exit pupils of theuser's eyes. That value may be called the eye relief and corresponds tothe distance between the exit pupil of the user's eye and the displayworn by the user in front of the eye. In practice, the value for the eyerelief may be a normalized value used generally for all viewers. Forexample, the eye relief may be assumed to be 20 mm and a depth planethat is at a depth of 1 m may be at a distance of 980 mm in front of thedisplay.

With reference now to FIGS. 4C and 4D, examples of matchedaccommodation-vergence distances and mismatched accommodation-vergencedistances are illustrated, respectively. As illustrated in FIG. 4C, thedisplay system may provide images of a virtual object to each eye 210,220. The images may cause the eyes 210, 220 to assume a vergence statein which the eyes converge on a point 15 on a depth plane 240. Inaddition, the images may be formed by a light having a wavefrontcurvature corresponding to real objects at that depth plane 240. As aresult, the eyes 210, 220 assume an accommodative state in which theimages are in focus on the retinas of those eyes. Thus, the user mayperceive the virtual object as being at the point 15 on the depth plane240.

It will be appreciated that each of the accommodative and vergencestates of the eyes 210, 220 are associated with a particular distance onthe z-axis. For example, an object at a particular distance from theeyes 210, 220 causes those eyes to assume particular accommodativestates based upon the distances of the object. The distance associatedwith a particular accommodative state may be referred to as theaccommodation distance, A_(d). Similarly, there are particular vergencedistances, V_(d), associated with the eyes in particular vergencestates, or positions relative to one another. Where the accommodationdistance and the vergence distance match, the relationship betweenaccommodation and vergence may be said to be physiologically correct.This is considered to be the most comfortable scenario for a viewer.

In stereoscopic displays, however, the accommodation distance and thevergence distance may not always match. For example, as illustrated inFIG. 4D, images displayed to the eyes 210, 220 may be displayed withwavefront divergence corresponding to depth plane 240, and the eyes 210,220 may assume a particular accommodative state in which the points 15a, 15 b on that depth plane are in focus. However, the images displayedto the eyes 210, 220 may provide cues for vergence that cause the eyes210, 220 to converge on a point 15 that is not located on the depthplane 240. As a result, the accommodation distance corresponds to thedistance from the exit pupils of the eyes 210, 220 to the depth plane240, while the vergence distance corresponds to the larger distance fromthe exit pupils of the eyes 210, 220 to the point 15, in someembodiments. The accommodation distance is different from the vergencedistance. Consequently, there is an accommodation-vergence mismatch.Such a mismatch is considered undesirable and may cause discomfort inthe user. It will be appreciated that the mismatch corresponds todistance (e.g., V_(d)−A_(d)) and may be characterized using diopters.

In some embodiments, it will be appreciated that a reference point otherthan exit pupils of the eyes 210, 220 may be utilized for determiningdistance for determining accommodation-vergence mismatch, so long as thesame reference point is utilized for the accommodation distance and thevergence distance. For example, the distances could be measured from thecornea to the depth plane, from the retina to the depth plane, from theeyepiece (e.g., a waveguide of the display device) to the depth plane,from the center of rotation of an eye, and so on.

Without being limited by theory, it is believed that users may stillperceive accommodation-vergence mismatches of up to about 0.25 diopter,up to about 0.33 diopter, and up to about 0.5 diopter as beingphysiologically correct, without the mismatch itself causing significantdiscomfort. In some embodiments, display systems disclosed herein (e.g.,the display system 250, FIG. 6) present images to the viewer havingaccommodation-vergence mismatch of about 0.5 diopter or less. In someother embodiments, the accommodation-vergence mismatch of the imagesprovided by the display system is about 0.33 diopter or less. In yetother embodiments, the accommodation-vergence mismatch of the imagesprovided by the display system is about 0.25 diopter or less, includingabout 0.1 diopter or less.

FIG. 5 illustrates aspects of an approach for simulatingthree-dimensional imagery by modifying wavefront divergence. The displaysystem includes a waveguide 270 that is configured to receive light 770that is encoded with image information, and to output that light to theuser's eye 210. The waveguide 270 may output the light 650 with adefined amount of wavefront divergence corresponding to the wavefrontdivergence of a light field produced by a point on a desired depth plane240. In some embodiments, the same amount of wavefront divergence isprovided for all objects presented on that depth plane. In addition, itwill be illustrated that the other eye of the user may be provided withimage information from a similar waveguide.

In some embodiments, a single waveguide may be configured to outputlight with a set amount of wavefront divergence corresponding to asingle or limited number of depth planes and/or the waveguide may beconfigured to output light of a limited range of wavelengths.Consequently, in some embodiments, a plurality or stack of waveguidesmay be utilized to provide different amounts of wavefront divergence fordifferent depth planes and/or to output light of different ranges ofwavelengths. As used herein, it will be appreciated that a depth planemay follow the contours of a flat or a curved surface. In someembodiments, advantageously for simplicity, the depth planes may followthe contours of flat surfaces.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user. A display system 250 includes a stack ofwaveguides, or stacked waveguide assembly, 260 that may be utilized toprovide three-dimensional perception to the eye/brain using a pluralityof waveguides 270, 280, 290, 300, 310. It will be appreciated that thedisplay system 250 may be considered a light field display in someembodiments. In addition, the waveguide assembly 260 may also bereferred to as an eyepiece.

In some embodiments, the display system 250 may be configured to providesubstantially continuous cues to vergence and multiple discrete cues toaccommodation. The cues to vergence may be provided by displayingdifferent images to each of the eyes of the user, and the cues toaccommodation may be provided by outputting the light that forms theimages with selectable discrete amounts of wavefront divergence. Statedanother way, the display system 250 may be configured to output lightwith variable levels of wavefront divergence. In some embodiments, eachdiscrete level of wavefront divergence corresponds to a particular depthplane and may be provided by a particular one of the waveguides 270,280, 290, 300, 310.

With continued reference to FIG. 6, the waveguide assembly 260 may alsoinclude a plurality of features 320, 330, 340, 350 between thewaveguides. In some embodiments, the features 320, 330, 340, 350 may beone or more lenses. The waveguides 270, 280, 290, 300, 310 and/or theplurality of lenses 320, 330, 340, 350 may be configured to send imageinformation to the eye with various levels of wavefront curvature orlight ray divergence. Each waveguide level may be associated with aparticular depth plane and may be configured to output image informationcorresponding to that depth plane. Image injection devices 360, 370,380, 390, 400 may function as a source of light for the waveguides andmay be utilized to inject image information into the waveguides 270,280, 290, 300, 310, each of which may be configured, as describedherein, to distribute incoming light across each respective waveguide,for output toward the eye 210. Light exits an output surface 410, 420,430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 andis injected into a corresponding input surface 460, 470, 480, 490, 500of the waveguides 270, 280, 290, 300, 310. In some embodiments, each ofthe input surfaces 460, 470, 480, 490, 500 may be an edge of acorresponding waveguide, or may be part of a major surface of thecorresponding waveguide (that is, one of the waveguide surfaces directlyfacing the world 510 or the viewer's eye 210). It will be appreciatedthat the major surfaces of a waveguide correspond to the surfaces of thewaveguide between which the thickness of the waveguide extends. In someembodiments, a single beam of light (e.g. a collimated beam) may beinjected into each waveguide to output an entire field of clonedcollimated beams that are directed toward the eye 210 at particularangles (and amounts of divergence) corresponding to the depth planeassociated with a particular waveguide. In some embodiments, a singleone of the image injection devices 360, 370, 380, 390, 400 may beassociated with and inject light into a plurality (e.g., three) of thewaveguides 270, 280, 290, 300, 310.

In some embodiments, the image injection devices 360, 370, 380, 390, 400are discrete displays that each produce image information for injectioninto a corresponding waveguide 270, 280, 290, 300, 310, respectively. Insome other embodiments, the image injection devices 360, 370, 380, 390,400 are the output ends of a single multiplexed display which may, e.g.,pipe image information via one or more optical conduits (such as fiberoptic cables) to each of the image injection devices 360, 370, 380, 390,400. It will be appreciated that the image information provided by theimage injection devices 360, 370, 380, 390, 400 may include light ofdifferent wavelengths, or colors (e.g., different component colors, asdiscussed herein).

In some embodiments, the light injected into the waveguides 270, 280,290, 300, 310 is provided by a light projector system 520, whichcomprises a light module 530, which may include a light emitter, such asa light emitting diode (LED). The light from the light module 530 may bedirected to and modified by a light modulator 540, e.g., a spatial lightmodulator, via a beam splitter 550. The light modulator 540 may beconfigured to change the perceived intensity of the light injected intothe waveguides 270, 280, 290, 300, 310 to encode the light with imageinformation. Examples of spatial light modulators include liquid crystaldisplays (LCD) including a liquid crystal on silicon (LCOS) displays. Itwill be appreciated that the image injection devices 360, 370, 380, 390,400 are illustrated schematically and, in some embodiments, these imageinjection devices may represent different light paths and locations in acommon projection system configured to output light into associated onesof the waveguides 270, 280, 290, 300, 310. In some embodiments, thewaveguides of the waveguide assembly 260 may function as ideal lenswhile relaying light injected into the waveguides out to the user'seyes. In this conception, the object may be the spatial light modulator540 and the image may be the image on the depth plane.

In some embodiments, the display system 250 may be a scanning fiberdisplay comprising one or more scanning fibers configured to projectlight in various patterns (e.g., raster scan, spiral scan, Lissajouspatterns, etc.) into one or more waveguides 270, 280, 290, 300, 310 andultimately to the eye 210 of the viewer. In some embodiments, theillustrated image injection devices 360, 370, 380, 390, 400 mayschematically represent a single scanning fiber or a bundle of scanningfibers configured to inject light into one or a plurality of thewaveguides 270, 280, 290, 300, 310. In some other embodiments, theillustrated image injection devices 360, 370, 380, 390, 400 mayschematically represent a plurality of scanning fibers or a plurality ofbundles of scanning fibers, each of which are configured to inject lightinto an associated one of the waveguides 270, 280, 290, 300, 310. Itwill be appreciated that one or more optical fibers may be configured totransmit light from the light module 530 to the one or more waveguides270, 280, 290, 300, 310. It will be appreciated that one or moreintervening optical structures may be provided between the scanningfiber, or fibers, and the one or more waveguides 270, 280, 290, 300, 310to, e.g., redirect light exiting the scanning fiber into the one or morewaveguides 270, 280, 290, 300, 310.

A controller 560 controls the operation of one or more of the stackedwaveguide assembly 260, including operation of the image injectiondevices 360, 370, 380, 390, 400, the light source 530, and the lightmodulator 540. In some embodiments, the controller 560 is part of thelocal data processing module 140. The controller 560 includesprogramming (e.g., instructions in a non-transitory medium) thatregulates the timing and provision of image information to thewaveguides 270, 280, 290, 300, 310 according to, e.g., any of thevarious schemes disclosed herein. In some embodiments, the controllermay be a single integral device, or a distributed system connected bywired or wireless communication channels. The controller 560 may be partof the processing modules 140 or 150 (FIG. 9D) in some embodiments.

With continued reference to FIG. 6, the waveguides 270, 280, 290, 300,310 may be configured to propagate light within each respectivewaveguide by total internal reflection (TIR). The waveguides 270, 280,290, 300, 310 may each be planar or have another shape (e.g., curved),with major top and bottom surfaces and edges extending between thosemajor top and bottom surfaces. In the illustrated configuration, thewaveguides 270, 280, 290, 300, 310 may each include out-coupling opticalelements 570, 580, 590, 600, 610 that are configured to extract lightout of a waveguide by redirecting the light, propagating within eachrespective waveguide, out of the waveguide to output image informationto the eye 210. Extracted light may also be referred to as out-coupledlight and the out-coupling optical elements light may also be referredto light extracting optical elements. An extracted beam of light may beoutputted by the waveguide at locations at which the light propagatingin the waveguide strikes a light extracting optical element. Theout-coupling optical elements 570, 580, 590, 600, 610 may, for example,be gratings, including diffractive optical features, as discussedfurther herein. While illustrated disposed at the bottom major surfacesof the waveguides 270, 280, 290, 300, 310, for ease of description anddrawing clarity, in some embodiments, the out-coupling optical elements570, 580, 590, 600, 610 may be disposed at the top and/or bottom majorsurfaces, and/or may be disposed directly in the volume of thewaveguides 270, 280, 290, 300, 310, as discussed further herein. In someembodiments, the out-coupling optical elements 570, 580, 590, 600, 610may be formed in a layer of material that is attached to a transparentsubstrate to form the waveguides 270, 280, 290, 300, 310. In some otherembodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithicpiece of material and the out-coupling optical elements 570, 580, 590,600, 610 may be formed on a surface and/or in the interior of that pieceof material.

With continued reference to FIG. 6, as discussed herein, each waveguide270, 280, 290, 300, 310 is configured to output light to form an imagecorresponding to a particular depth plane. For example, the waveguide270 nearest the eye may be configured to deliver collimated light (whichwas injected into such waveguide 270), to the eye 210. The collimatedlight may be representative of the optical infinity focal plane. Thenext waveguide up 280 may be configured to send out collimated lightwhich passes through the first lens 350 (e.g., a negative lens) beforeit may reach the eye 210; such first lens 350 may be configured tocreate a slight convex wavefront curvature so that the eye/braininterprets light coming from that next waveguide up 280 as coming from afirst focal plane closer inward toward the eye 210 from opticalinfinity. Similarly, the third up waveguide 290 passes its output lightthrough both the first 350 and second 340 lenses before reaching the eye210 the combined optical power of the first 350 and second 340 lensesmay be configured to create another incremental amount of wavefrontcurvature so that the eye/brain interprets light coming from the thirdwaveguide 290 as coming from a second focal plane that is even closerinward toward the person from optical infinity than was light from thenext waveguide up 280.

The other waveguide layers 300, 310 and lenses 330, 320 are similarlyconfigured, with the highest waveguide 310 in the stack sending itsoutput through all of the lenses between it and the eye for an aggregatefocal power representative of the closest focal plane to the person. Tocompensate for the stack of lenses 320, 330, 340, 350 whenviewing/interpreting light coming from the world 510 on the other sideof the stacked waveguide assembly 260, a compensating lens layer 620 maybe disposed at the top of the stack to compensate for the aggregatepower of the lens stack 320, 330, 340, 350 below. Such a configurationprovides as many perceived focal planes as there are availablewaveguide/lens pairings. Both the out-coupling optical elements of thewaveguides and the focusing aspects of the lenses may be static (i.e.,not dynamic or electro-active). In some alternative embodiments, eitheror both may be dynamic using electro-active features.

In some embodiments, two or more of the waveguides 270, 280, 290, 300,310 may have the same associated depth plane. For example, multiplewaveguides 270, 280, 290, 300, 310 may be configured to output imagesset to the same depth plane, or multiple subsets of the waveguides 270,280, 290, 300, 310 may be configured to output images set to the sameplurality of depth planes, with one set for each depth plane. This mayprovide advantages for forming a tiled image to provide an expandedfield of view at those depth planes.

With continued reference to FIG. 6, the out-coupling optical elements570, 580, 590, 600, 610 may be configured to both redirect light out oftheir respective waveguides and to output this light with theappropriate amount of divergence or collimation for a particular depthplane associated with the waveguide. As a result, waveguides havingdifferent associated depth planes may have different configurations ofout-coupling optical elements 570, 580, 590, 600, 610, which outputlight with a different amount of divergence depending on the associateddepth plane. In some embodiments, the light extracting optical elements570, 580, 590, 600, 610 may be volumetric or surface features, which maybe configured to output light at specific angles. For example, the lightextracting optical elements 570, 580, 590, 600, 610 may be volumeholograms, surface holograms, and/or diffraction gratings. In someembodiments, the features 320, 330, 340, 350 may not be lenses; rather,they may simply be spacers (e.g., cladding layers and/or structures forforming air gaps).

In some embodiments, the out-coupling optical elements 570, 580, 590,600, 610 are diffractive features that form a diffraction pattern, or“diffractive optical element” (also referred to herein as a “DOE”).Preferably, the DOE's have a sufficiently low diffraction efficiency sothat only a portion of the light of the beam is deflected away towardthe eye 210 with each intersection of the DOE, while the rest continuesto move through a waveguide via TIR. The light carrying the imageinformation is thus divided into a number of related exit beams thatexit the waveguide at a multiplicity of locations and the result is afairly uniform pattern of exit emission toward the eye 210 for thisparticular collimated beam bouncing around within a waveguide.

In some embodiments, one or more DOEs may be switchable between “on”states in which they actively diffract, and “off” states in which theydo not significantly diffract. For instance, a switchable DOE maycomprise a layer of polymer dispersed liquid crystal, in whichmicrodroplets comprise a diffraction pattern in a host medium, and therefractive index of the microdroplets may be switched to substantiallymatch the refractive index of the host material (in which case thepattern does not appreciably diffract incident light) or themicrodroplet may be switched to an index that does not match that of thehost medium (in which case the pattern actively diffracts incidentlight).

In some embodiments, a camera assembly 630 (e.g., a digital camera,including visible light and infrared light cameras) may be provided tocapture images of the eye 210 and/or tissue around the eye 210 to, e.g.,detect user inputs and/or to monitor the physiological state of theuser. As used herein, a camera may be any image capture device. In someembodiments, the camera assembly 630 may include an image capture deviceand a light source to project light (e.g., infrared light) to the eye,which may then be reflected by the eye and detected by the image capturedevice. In some embodiments, the camera assembly 630 may be attached tothe frame 80 (FIG. 9D) and may be in electrical communication with theprocessing modules 140 and/or 150, which may process image informationfrom the camera assembly 630. In some embodiments, one camera assembly630 may be utilized for each eye, to separately monitor each eye.

With reference now to FIG. 7, an example of exit beams outputted by awaveguide is shown. One waveguide is illustrated, but it will beappreciated that other waveguides in the waveguide assembly 260 (FIG. 6)may function similarly, where the waveguide assembly 260 includesmultiple waveguides. Light 640 is injected into the waveguide 270 at theinput surface 460 of the waveguide 270 and propagates within thewaveguide 270 by TIR. At points where the light 640 impinges on the DOE570, a portion of the light exits the waveguide as exit beams 650. Theexit beams 650 are illustrated as substantially parallel but, asdiscussed herein, they may also be redirected to propagate to the eye210 at an angle (e.g., forming divergent exit beams), depending on thedepth plane associated with the waveguide 270. It will be appreciatedthat substantially parallel exit beams may be indicative of a waveguidewith out-coupling optical elements that out-couple light to form imagesthat appear to be set on a depth plane at a large distance (e.g.,optical infinity) from the eye 210. Other waveguides or other sets ofout-coupling optical elements may output an exit beam pattern that ismore divergent, which would require the eye 210 to accommodate to acloser distance to bring it into focus on the retina and would beinterpreted by the brain as light from a distance closer to the eye 210than optical infinity.

In some embodiments, a full color image may be formed at each depthplane by overlaying images in each of the component colors, e.g., threeor more component colors. FIG. 8 illustrates an example of a stackedwaveguide assembly in which each depth plane includes images formedusing multiple different component colors. The illustrated embodimentshows depth planes 240 a-240 f, although more or fewer depths are alsocontemplated. Each depth plane may have three or more component colorimages associated with it, including: a first image of a first color, G;a second image of a second color, R; and a third image of a third color,B. Different depth planes are indicated in the figure by differentnumbers for diopters (dpt) following the letters G, R, and B. Just asexamples, the numbers following each of these letters indicate diopters(1/m), or inverse distance of the depth plane from a viewer, and eachbox in the figures represents an individual component color image. Insome embodiments, to account for differences in the eye's focusing oflight of different wavelengths, the exact placement of the depth planesfor different component colors may vary. For example, differentcomponent color images for a given depth plane may be placed on depthplanes corresponding to different distances from the user. Such anarrangement may increase visual acuity and user comfort and/or maydecrease chromatic aberrations.

In some embodiments, light of each component color may be outputted by asingle dedicated waveguide and, consequently, each depth plane may havemultiple waveguides associated with it. In such embodiments, each box inthe figures including the letters G, R, or B may be understood torepresent an individual waveguide, and three waveguides may be providedper depth plane where three component color images are provided perdepth plane. While the waveguides associated with each depth plane areshown adjacent to one another in this drawing for ease of description,it will be appreciated that, in a physical device, the waveguides mayall be arranged in a stack with one waveguide per level. In some otherembodiments, multiple component colors may be outputted by the samewaveguide, such that, e.g., only a single waveguide may be provided perdepth plane.

With continued reference to FIG. 8, in some embodiments, G is the colorgreen, R is the color red, and B is the color blue. In some otherembodiments, other colors associated with other wavelengths of light,including magenta and cyan, may be used in addition to or may replaceone or more of red, green, or blue.

It will be appreciated that references to a given color of lightthroughout this disclosure will be understood to encompass light of oneor more wavelengths within a range of wavelengths of light that areperceived by a viewer as being of that given color. For example, redlight may include light of one or more wavelengths in the range of about620-780 nm, green light may include light of one or more wavelengths inthe range of about 492-577 nm, and blue light may include light of oneor more wavelengths in the range of about 435-493 nm.

In some embodiments, the light source 530 (FIG. 6) may be configured toemit light of one or more wavelengths outside the visual perceptionrange of the viewer, for example, infrared and/or ultravioletwavelengths. In addition, the in-coupling, out-coupling, and other lightredirecting structures of the waveguides of the display 250 may beconfigured to direct and emit this light out of the display towards theuser's eye 210, e.g., for imaging and/or user stimulation applications.

With reference now to FIG. 9A, in some embodiments, light impinging on awaveguide may need to be redirected to in-couple that light into thewaveguide. An in-coupling optical element may be used to redirect andin-couple the light into its corresponding waveguide. FIG. 9Aillustrates a cross-sectional side view of an example of a plurality orset 660 of stacked waveguides that each includes an in-coupling opticalelement. The waveguides may each be configured to output light of one ormore different wavelengths, or one or more different ranges ofwavelengths. It will be appreciated that the stack 660 may correspond tothe stack 260 (FIG. 6) and the illustrated waveguides of the stack 660may correspond to part of the plurality of waveguides 270, 280, 290,300, 310, except that light from one or more of the image injectiondevices 360, 370, 380, 390, 400 is injected into the waveguides from aposition that requires light to be redirected for in-coupling.

The illustrated set 660 of stacked waveguides includes waveguides 670,680, and 690. Each waveguide includes an associated in-coupling opticalelement (which may also be referred to as a light input area on thewaveguide), with, e.g., in-coupling optical element 700 disposed on amajor surface (e.g., an upper major surface) of waveguide 670,in-coupling optical element 710 disposed on a major surface (e.g., anupper major surface) of waveguide 680, and in-coupling optical element720 disposed on a major surface (e.g., an upper major surface) ofwaveguide 690. In some embodiments, one or more of the in-couplingoptical elements 700, 710, 720 may be disposed on the bottom majorsurface of the respective waveguide 670, 680, 690 (particularly wherethe one or more in-coupling optical elements are reflective, deflectingoptical elements). As illustrated, the in-coupling optical elements 700,710, 720 may be disposed on the upper major surface of their respectivewaveguide 670, 680, 690 (or the top of the next lower waveguide),particularly where those in-coupling optical elements are transmissive,deflecting optical elements. In some embodiments, the in-couplingoptical elements 700, 710, 720 may be disposed in the body of therespective waveguide 670, 680, 690. In some embodiments, as discussedherein, the in-coupling optical elements 700, 710, 720 are wavelengthselective, such that they selectively redirect one or more wavelengthsof light, while transmitting other wavelengths of light. Whileillustrated on one side or corner of their respective waveguide 670,680, 690, it will be appreciated that the in-coupling optical elements700, 710, 720 may be disposed in other areas of their respectivewaveguide 670, 680, 690 in some embodiments.

As illustrated, the in-coupling optical elements 700, 710, 720 may belaterally offset from one another. In some embodiments, each in-couplingoptical element may be offset such that it receives light without thatlight passing through another in-coupling optical element. For example,each in-coupling optical element 700, 710, 720 may be configured toreceive light from a different image injection device 360, 370, 380,390, and 400 as shown in FIG. 6, and may be separated (e.g., laterallyspaced apart) from other in-coupling optical elements 700, 710, 720 suchthat it substantially does not receive light from the other ones of thein-coupling optical elements 700, 710, 720.

Each waveguide also includes associated light distributing elements,with, e.g., light distributing elements 730 disposed on a major surface(e.g., a top major surface) of waveguide 670, light distributingelements 740 disposed on a major surface (e.g., a top major surface) ofwaveguide 680, and light distributing elements 750 disposed on a majorsurface (e.g., a top major surface) of waveguide 690. In some otherembodiments, the light distributing elements 730, 740, 750, may bedisposed on a bottom major surface of associated waveguides 670, 680,690, respectively. In some other embodiments, the light distributingelements 730, 740, 750, may be disposed on both top and bottom majorsurface of associated waveguides 670, 680, 690, respectively; or thelight distributing elements 730, 740, 750, may be disposed on differentones of the top and bottom major surfaces in different associatedwaveguides 670, 680, 690, respectively.

The waveguides 670, 680, 690 may be spaced apart and separated by, e.g.,gas, liquid, and/or solid layers of material. For example, asillustrated, layer 760 a may separate waveguides 670 and 680; and layer760 b may separate waveguides 680 and 690. In some embodiments, thelayers 760 a and 760 b are formed of low refractive index materials(that is, materials having a lower refractive index than the materialforming the immediately adjacent one of waveguides 670, 680, 690).Preferably, the refractive index of the material forming the layers 760a, 760 b is 0.05 or more, or 0.10 or less than the refractive index ofthe material forming the waveguides 670, 680, 690. Advantageously, thelower refractive index layers 760 a, 760 b may function as claddinglayers that facilitate total internal reflection (TIR) of light throughthe waveguides 670, 680, 690 (e.g., TIR between the top and bottom majorsurfaces of each waveguide). In some embodiments, the layers 760 a, 760b are formed of air. While not illustrated, it will be appreciated thatthe top and bottom of the illustrated set 660 of waveguides may includeimmediately neighboring cladding layers.

Preferably, for ease of manufacturing and other considerations, thematerial forming the waveguides 670, 680, 690 are similar or the same,and the material forming the layers 760 a, 760 b are similar or thesame. In some embodiments, the material forming the waveguides 670, 680,690 may be different between one or more waveguides, and/or the materialforming the layers 760 a, 760 b may be different, while still holding tothe various refractive index relationships noted above.

With continued reference to FIG. 9A, light rays 770, 780, 790 areincident on the set 660 of waveguides. It will be appreciated that thelight rays 770, 780, 790 may be injected into the waveguides 670, 680,690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG.6).

In some embodiments, the light rays 770, 780, 790 have differentproperties, e.g., different wavelengths or different ranges ofwavelengths, which may correspond to different colors. The incouplingoptical elements 700, 710, 720 each deflect the incident light such thatthe light propagates through a respective one of the waveguides 670,680, 690 by TIR. In some embodiments, the incoupling optical elements700, 710, 720 each selectively deflect one or more particularwavelengths of light, while transmitting other wavelengths to anunderlying waveguide and associated incoupling optical element.

For example, in-coupling optical element 700 may be configured todeflect ray 770, which has a first wavelength or range of wavelengths,while transmitting rays 780 and 790, which have different second andthird wavelengths or ranges of wavelengths, respectively. Thetransmitted ray 780 impinges on and is deflected by the in-couplingoptical element 710, which is configured to deflect light of a secondwavelength or range of wavelengths. The ray 790 is deflected by thein-coupling optical element 720, which is configured to selectivelydeflect light of third wavelength or range of wavelengths.

With continued reference to FIG. 9A, the deflected light rays 770, 780,790 are deflected so that they propagate through a correspondingwaveguide 670, 680, 690; that is, the in-coupling optical elements 700,710, 720 of each waveguide deflects light into that correspondingwaveguide 670, 680, 690 to in-couple light into that correspondingwaveguide. The light rays 770, 780, 790 are deflected at angles thatcause the light to propagate through the respective waveguide 670, 680,690 by TIR. The light rays 770, 780, 790 propagate through therespective waveguide 670, 680, 690 by TIR until impinging on thewaveguide's corresponding light distributing elements 730, 740, 750.

With reference now to FIG. 9B, a perspective view of an example of theplurality of stacked waveguides of FIG. 9A is illustrated. As notedabove, the in-coupled light rays 770, 780, 790, are deflected by thein-coupling optical elements 700, 710, 720, respectively, and thenpropagate by TIR within the waveguides 670, 680, 690, respectively. Thelight rays 770, 780, 790 then impinge on the light distributing elements730, 740, 750, respectively. The light distributing elements 730, 740,750 deflect the light rays 770, 780, 790 so that they propagate towardsthe out-coupling optical elements 800, 810, 820, respectively.

In some embodiments, the light distributing elements 730, 740, 750 areorthogonal pupil expanders (OPE's). In some embodiments, the OPE'sdeflect or distribute light to the out-coupling optical elements 800,810, 820 and, in some embodiments, may also increase the beam or spotsize of this light as it propagates to the out-coupling opticalelements. In some embodiments, the light distributing elements 730, 740,750 may be omitted and the in-coupling optical elements 700, 710, 720may be configured to deflect light directly to the out-coupling opticalelements 800, 810, 820. For example, with reference to FIG. 9A, thelight distributing elements 730, 740, 750 may be replaced without-coupling optical elements 800, 810, 820, respectively. In someembodiments, the out-coupling optical elements 800, 810, 820 are exitpupils (EP's) or exit pupil expanders (EPE's) that direct light in aviewer's eye 210 (FIG. 7). It will be appreciated that the OPE's may beconfigured to increase the dimensions of the eye box in at least oneaxis and the EPE's may be to increase the eye box in an axis crossing,e.g., orthogonal to, the axis of the OPEs. For example, each OPE may beconfigured to redirect a portion of the light striking the OPE to an EPEof the same waveguide, while allowing the remaining portion of the lightto continue to propagate down the waveguide. Upon impinging on the OPEagain, another portion of the remaining light is redirected to the EPE,and the remaining portion of that portion continues to propagate furtherdown the waveguide, and so on. Similarly, upon striking the EPE, aportion of the impinging light is directed out of the waveguide towardsthe user, and a remaining portion of that light continues to propagatethrough the waveguide until it strikes the EP again, at which timeanother portion of the impinging light is directed out of the waveguide,and so on. Consequently, a single beam of incoupled light may be“replicated” each time a portion of that light is redirected by an OPEor EPE, thereby forming a field of cloned beams of light, as shown inFIG. 6. In some embodiments, the OPE and/or EPE may be configured tomodify a size of the beams of light.

Accordingly, with reference to FIGS. 9A and 9B, in some embodiments, theset 660 of waveguides includes waveguides 670, 680, 690; in-couplingoptical elements 700, 710, 720; light distributing elements (e.g.,OPE's) 730, 740, 750; and out-coupling optical elements (e.g., EP's)800, 810, 820 for each component color. The waveguides 670, 680, 690 maybe stacked with an air gap/cladding layer between each one. Thein-coupling optical elements 700, 710, 720 redirect or deflect incidentlight (with different in-coupling optical elements receiving light ofdifferent wavelengths) into its waveguide. The light then propagates atan angle which will result in TIR within the respective waveguide 670,680, 690. In the example shown, light ray 770 (e.g., blue light) isdeflected by the first in-coupling optical element 700, and thencontinues to bounce down the waveguide, interacting with the lightdistributing element (e.g., OPE's) 730 and then the out-coupling opticalelement (e.g., EPs) 800, in a manner described earlier. The light rays780 and 790 (e.g., green and red light, respectively) will pass throughthe waveguide 670, with light ray 780 impinging on and being deflectedby in-coupling optical element 710. The light ray 780 then bounces downthe waveguide 680 via TIR, proceeding on to its light distributingelement (e.g., OPEs) 740 and then the out-coupling optical element(e.g., EP's) 810. Finally, light ray 790 (e.g., red light) passesthrough the waveguide 690 to impinge on the light in-coupling opticalelements 720 of the waveguide 690. The light in-coupling opticalelements 720 deflect the light ray 790 such that the light raypropagates to light distributing element (e.g., OPEs) 750 by TIR, andthen to the out-coupling optical element (e.g., EPs) 820 by TIR. Theout-coupling optical element 820 then finally out-couples the light ray790 to the viewer, who also receives the out-coupled light from theother waveguides 670, 680.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B. As illustrated, the waveguides670, 680, 690, along with each waveguide's associated light distributingelement 730, 740, 750 and associated out-coupling optical element 800,810, 820, may be vertically aligned. However, as discussed herein, thein-coupling optical elements 700, 710, 720 are not vertically aligned;rather, the in-coupling optical elements are preferably non-overlapping(e.g., laterally spaced apart as seen in the top-down view). Asdiscussed further herein, this nonoverlapping spatial arrangementfacilitates the injection of light from different resources intodifferent waveguides on a one-to-one basis, thereby allowing a specificlight source to be uniquely coupled to a specific waveguide. In someembodiments, arrangements including nonoverlapping spatially-separatedin-coupling optical elements may be referred to as a shifted pupilsystem, and the in-coupling optical elements within these arrangementsmay correspond to sub pupils.

FIG. 9D illustrates an example of wearable display system 60 into whichthe various waveguides and related systems disclosed herein may beintegrated. In some embodiments, the display system 60 is the system 250of FIG. 6, with FIG. 6 schematically showing some parts of that system60 in greater detail. For example, the waveguide assembly 260 of FIG. 6may be part of the display 70.

With continued reference to FIG. 9D, the display system 60 includes adisplay 70, and various mechanical and electronic modules and systems tosupport the functioning of that display 70. The display 70 may becoupled to a frame 80, which is wearable by a display system user orviewer 90 and which is configured to position the display 70 in front ofthe eyes of the user 90. The display 70 may be considered eyewear insome embodiments. In some embodiments, a speaker 100 is coupled to theframe 80 and configured to be positioned adjacent the ear canal of theuser 90 (in some embodiments, another speaker, not shown, may optionallybe positioned adjacent the other ear canal of the user to providestereo/shapeable sound control). The display system 60 may also includeone or more microphones 110 or other devices to detect sound. In someembodiments, the microphone is configured to allow the user to provideinputs or commands to the system 60 (e.g., the selection of voice menucommands, natural language questions, etc.), and/or may allow audiocommunication with other persons (e.g., with other users of similardisplay systems. The microphone may further be configured as aperipheral sensor to collect audio data (e.g., sounds from the userand/or environment). In some embodiments, the display system 60 mayfurther include one or more outwardly-directed environmental sensors 112configured to detect objects, stimuli, people, animals, locations, orother aspects of the world around the user. For example, environmentalsensors 112 may include one or more cameras, which may be located, forexample, facing outward so as to capture images similar to at least aportion of an ordinary field of view of the user 90. In someembodiments, the display system may also include a peripheral sensor 120a, which may be separate from the frame 80 and attached to the body ofthe user 90 (e.g., on the head, torso, an extremity, etc. of the user90). The peripheral sensor 120 a may be configured to acquire datacharacterizing a physiological state of the user 90 in some embodiments.For example, the sensor 120 a may be an electrode.

With continued reference to FIG. 9D, the display 70 is operativelycoupled by communications link 130, such as by a wired lead or wirelessconnectivity, to a local data processing module 140 which may be mountedin a variety of configurations, such as fixedly attached to the frame80, fixedly attached to a helmet or hat worn by the user, embedded inheadphones, or otherwise removably attached to the user 90 (e.g., in abackpack-style configuration, in a belt-coupling style configuration).Similarly, the sensor 120 a may be operatively coupled by communicationslink 120 b, e.g., a wired lead or wireless connectivity, to the localprocessor and data module 140. The local processing and data module 140may comprise a hardware processor, as well as digital memory, such asnon-volatile memory (e.g., flash memory or hard disk drives), both ofwhich may be utilized to assist in the processing, caching, and storageof data. Optionally, the local processor and data module 140 may includeone or more central processing units (CPUs), graphics processing units(GPUs), dedicated processing hardware, and so on. The data may includedata a) captured from sensors (which may be, e.g., operatively coupledto the frame 80 or otherwise attached to the user 90), such as imagecapture devices (such as cameras), microphones, inertial measurementunits, accelerometers, compasses, GPS units, radio devices, gyros,and/or other sensors disclosed herein; and/or b) acquired and/orprocessed using remote processing module 150 and/or remote datarepository 160 (including data relating to virtual content), possiblyfor passage to the display 70 after such processing or retrieval. Thelocal processing and data module 140 may be operatively coupled bycommunication links 170, 180, such as via a wired or wirelesscommunication links, to the remote processing module 150 and remote datarepository 160 such that these remote modules 150, 160 are operativelycoupled to each other and available as resources to the local processingand data module 140. In some embodiments, the local processing and datamodule 140 may include one or more of the image capture devices,microphones, inertial measurement units, accelerometers, compasses, GPSunits, radio devices, and/or gyros. In some other embodiments, one ormore of these sensors may be attached to the frame 80, or may bestandalone structures that communicate with the local processing anddata module 140 by wired or wireless communication pathways.

With continued reference to FIG. 9D, in some embodiments, the remoteprocessing module 150 may comprise one or more processors configured toanalyze and process data and/or image information, for instanceincluding one or more central processing units (CPUs), graphicsprocessing units (GPUs), dedicated processing hardware, and so on. Insome embodiments, the remote data repository 160 may comprise a digitaldata storage facility, which may be available through the internet orother networking configuration in a “cloud” resource configuration. Insome embodiments, the remote data repository 160 may include one or moreremote servers, which provide information, e.g., information forgenerating augmented reality content, to the local processing and datamodule 140 and/or the remote processing module 150. In some embodiments,all data is stored and all computations are performed in the localprocessing and data module, allowing fully autonomous use from a remotemodule. Optionally, an outside system (e.g., a system of one or moreprocessors, one or more computers) that includes CPUs, GPUs, and so on,may perform at least a portion of processing (e.g., generating imageinformation, processing data) and provide information to, and receiveinformation from, modules 140, 150, 160, for instance via wireless orwired connections.

Example Waveguide Structures

Referring now to FIG. 10A, an example of a waveguide comprising spacersis illustrated. A waveguide 1000 comprises a main optically transmissivebody 1010 and spacers 1020 extending vertically from a major surface1022 of the main body 1010. Preferably, the spacers 1020 are integralwith the waveguide 1000 and form a monolithic structure with at least apart of the waveguide defining the major surface 1022. More preferably,the spacers 1020 form a monolithic structure with the entire waveguide1000, with the material of the waveguide 1000 extending vertically toform the spacers 1020. As a result, the spacers 1020 and main body 1010may be formed of the same material and be without an interveningboundary.

In some embodiments, the spacers 1020 may be formed of a differentmaterial than the main body 1010, such that an intervening boundaryexists at the interface of the spacers 1020 and the main body 1010. Forexample, the spacers 1020 may comprise locally deposited material, whichis then imprinted to form the spacers 1020.

In some embodiments, indentations 1030 are provided extending into amajor surface 1032 of the waveguide 1000. As illustrated, the majorsurface 1032 and, thus, the indentations 1030 are disposed on a side ofthe waveguide 1000 opposite the major surface 1022. As discussed furtherherein, the indentations 1030 are preferably positioned, shaped, andsized such that spacers of an underlying waveguide (not illustrated) maybe accommodated within those indentations 1030. Similarly, the spacers1020 are preferably position, shaped, and sized such that they may beaccommodated within indentations of an overlying waveguide (notillustrated). In some embodiments, the waveguide 1000 may be providedwithout indentations 1030 and any underlying spacers may simply contactthe major surface 1032.

With continued reference to FIG. 10A, in some embodiments, the majorsurface 1022 may comprise surface relief features 1040. As illustrated,the spacers 1020 extend vertically to a height greater than the top ofthe surface relief features 1040. Preferably, the spacers 1020 have aheight sufficient to space the waveguide 1000 from an overlyingwaveguide by a desired separation distance, e.g., 30 μm or more. In someembodiments, the spacers 1020 have a height of 30 μm or more. Asdiscussed herein, the spacers 1020 may fit within the indentations 1030of an overlying waveguide in some embodiments. In such embodiments, theheight of the spacers 1020 may be equal to the desired separationbetween waveguides (e.g., 30 μm) plus the height of the indentations inwhich the spacers are inserted.

Additionally or alternatively to the surface relief features 1040, insome embodiments, the opposing major surface 1032 may comprise surfacerelief features 1050. In some embodiments, one or both of the surfacerelief features 1040 and 1050 may include a pattern of protrusions andindentations sized and arranged to form a diffractive optical element,such as diffractive gratings. It will be appreciated that suchdiffractive optical elements may correspond to one or more of thein-coupling optical elements 700, 710, 720; light distributing elements730, 740, 750; or out-coupling optical elements 800, 810, 820 of FIGS.9A-9C. In some embodiments, the waveguide 1000 may omit one or both ofthe surface relief features 1040, 1050 such that the major surfaces1022, 1032 may be smooth except for spacers 1020, 1030, respectively.

In some embodiments, the surface relief features 1040, 1050 mayadvantageously increase the density of surface relief features across agiven expanse of the waveguide 1000 and may be identical. In some otherembodiments, the surface relief features 1040, 1050 may be different.For example, the surface relief features 1040 may be configured todiffract light of different wavelengths and/or different incident anglesand/or to output light at different angles from the surface relieffeatures 1050.

With continued reference to FIG. 10A, the waveguide 1000 is formed of anoptically transmissive material, e.g., a highly transparent material.Preferably, the material has a high refractive index, which may provideadvantages for providing a large field of view. In some embodiments, thematerial has a refractive index greater than 1.5, or greater than 1.65.The material forming the waveguide 1000 may be a highly transparentpolymer material, e.g., an organic polymer material. Examples of highrefractive index materials include polyimide-based high index resins,halogen-containing (e.g., bromine or iodine-containing) polymers,phosphorous containing polymers, thiol-ene based polymers, and highrefractive index resin materials. Examples of high refractive indexresin materials include those commercially available from NTT-AT ofKawasaki-shi, Kanagawa, Japan, such as the high refractive index resinssold under the name #565 and #566; and high refractive index resinmaterials commercially available from Akron Polymer System of Akron,Ohio, USA, such as the high refractive index resins sold under the nameAPS-1000, APS2004, APS-4001, and as part of the APS 3000 series.

With reference now to FIG. 10B, examples of 3-dimensional shapes forspacers and indentations for accommodating the spacers are illustrated.In some embodiments, the spacers 1020 and corresponding indentations1030 may be laterally-elongated three-dimensional volumes. It will beappreciated that such laterally-elongated volumes may provide advantagesfor structural stability and mechanical strength, particularly where thewaveguides are utilized to form stacks of similar waveguides. An exampleof such a laterally-elongated three-dimensional volume is shape A, arectangular prism. In some embodiments, the spacers 1020 andcorresponding indentations 1030 may have other shapes includingrectangular prisms (shape B), cylinders (shape C), rectangular pyramids(shape D), triangular pyramids (shape E), and cones (shape F). It willbe appreciated that, in a single waveguide and/or a stack of waveguides,multiple different shapes may be utilized in some embodiments. In someembodiments, the tops of the spacers 1020, having a pointed shape (e.g.,a rectangular pyramid (shape D), a triangular pyramid (shape E), or acone (shape F)), may be rounded or flattened to reduce stress at thepoint of contact with an overlying structure such as another waveguide.Where the spacers 1020 are formed by imprinting, the desired rounding orflattening of the tops of the shapes may be formed by an appropriatelyshaped mold or imprint reticle.

With reference now to FIG. 10C, an example of a stack of waveguidescomprising spacers as illustrated. A stack 1100 of waveguides comprisesindividual waveguides 1000 a, 1000 b, and 1000 c have, respectively,optically transmissive bodies 1010 a, 1010 b, 1010 c. Each waveguidecomprises, respectively, spacers 1020 a, 1020 b, 1020 c. Preferably,each waveguide also comprises, respectively, indentations 1030 a, 1030b, 1030 c for accommodating the spacers of a directly underlyingwaveguide. It will be appreciated that the spacers have a height greaterthan the depth of the indentations, such that, once accommodated intothe indentations, the spacers separate the waveguides by a gap (e.g., anair gap). As illustrated, the spacers 1020 b fit within the indentations1030 a, and the spacers 1020 c fit within the indentations 1030 b.

In some embodiments, one or more of the waveguides 1000 a, 1000 b, 1000c may comprise surface relief features on one or more major surfaces ofthose waveguides. For example, each of these waveguides may comprisesurface relief features 1040 a, 1050 b corresponding to the surfacerelief features 1040, 1050 of the waveguide 1000 (FIG. 10A). In someembodiments, different ones of the waveguides 1000 a, 1000 b, 1000 c mayinclude diffractive optical elements configured to incouple and/oroutcouple light of different wavelengths, e.g., corresponding todifferent component colors for forming a full-color image. For example,the waveguides 1000 a, 1000 b, 1000 c may correspond to the waveguides670, 680, 690 of FIGS. 9A-9C.

It will be appreciated that light may propagate through the waveguides1000 a, 1000 b, 1000 c by total internal reflection, e.g., fromincoupling optical elements to outcoupling optical elements. Inaddition, light leakage between the waveguides may degrade imagequality. To reduce the likelihood that the spacers 1020, 1020 a, 1020 b,1020 c may be conduits for light leakage between waveguides, the spacers1020, 1020 a, 1020 b, 1020 c are preferably disposed at locations thatare out of the path of propagation of light between incoupling opticalelements and outcoupling optical elements.

In some embodiments, light leakage between waveguides may be mitigatedusing one or both of light scattering features and light leakageprevention materials at the interface between spacers 1020, 1020 a, 1020b, 1020 c and immediately adjacent waveguides. Examples of light leakageprevention materials include light absorbing materials and layers ofmaterial forming anti-reflective coatings. FIG. 11A illustrates anexample of a waveguide comprising spacers 1020 with light scatteringfeatures 1060 on surfaces of the spacers that are configured tointerface with an overlying waveguide. In some embodiments, the lightscattering features 1060 may take the form of peaks and valleys (e.g.,irregularly oriented peaks and valleys) on the surface of the spacers1020. In some embodiments, the light scattering features 1060 may beprovided only on top surfaces of the spacers. In some other embodiments,the light scattering features 1060 may also extend on the sides of thespacers 1020. It will be appreciated that light scattering features 1060may be formed by roughening surfaces of the spacers 1020, e.g., byabrasion. In some embodiments, the light scattering features 1060 may beformed during the formation of the spacers 1020. For example, spacers1020 may be formed by imprinting, and the mold used to form the spacers1020 may include a pattern to form the light scattering features 1060 atthe tops of the spacers 1020 thereby advantageously allowingsimultaneous formation of the waveguide features (e.g., diffractiveoptical elements 1040), spacers 1020, and the light scattering features1060. It will be appreciated that conventional waveguide materials suchas glasses are generally considered not compatible with suchsimultaneous formation, due to concerns regarding breakage of discreteintegral protrusions such as spacers and an inability to accuratelyreproduce the constituent features that form the diffractive opticalelements 1040 and light scattering features 1060.

As noted above, in some embodiments, one or more layers of material maybe utilized to prevent light leakage between spacers and waveguides.FIG. 11B illustrates an example of a stack of waveguides 1100 comprisingspacers 1020 a, 1020 b, 1020 c and light leakage prevention material1070 at the interface between the spacers and immediately neighboringones of the waveguides 1000 a, 1000 b, 1000 c. For example, lightleakage prevention material 1070 may be a light absorbing materialand/or one or more layers of material forming an antireflective coating.The light leakage prevention material 1070 may be provided betweenspacers 1020 b and waveguide 1000 a. Light leakage prevention material1070 may also be provided between spacers 1020 c and waveguide 1000 b.In some embodiments, the light leakage prevention material 1070 may beapplied to the spacers before attaching the spacers to anotherwaveguide. For example, light leakage prevention material 1070 may bedeposited on surfaces of the spacers before inserting the spacers intomatching indentations in an overlying waveguide. Examples of lightabsorbing materials to serve as the light leakage prevention material1070 include carbon black, meso-porous carbon, carbon nanotubes(single-walled as well as multi-walled nanotubes). Example of carbonnanotubes include single atom carbon nanotubes such as VANTA BLACK®available from Surrey NanoSystems of Newhaven, the United Kingdom. Insome embodiments, the light leakage prevention material 1070 may be alight absorbing adhesive which may be used to adhere the spacers to anoverlying waveguide. In some embodiments, the spacers may include lightscattering features and light leakage prevention materials at theinterface between the spacers and an overlying waveguide.

With continued reference to FIG. 11B, the light leakage preventionmaterial 1070 may form an anti-reflective coating. Examples ofanti-reflective coatings include single and multi-layer anti-reflectivecoatings formed of partially reflective and partially transmissivelayers of material.

With reference now to FIGS. 12A-12C, an example of a method for forminga waveguide with spacers as illustrated. With reference to FIG. 12A, apair of molds 1200, 1202 is provided. The mold 1202 comprises a patternof raised features 1250, which may be the negative of a desired patternto be defined in the waveguide to be formed. In some embodiments, themold 1202 includes a plurality of raised features 1230 for formingindentations in the waveguide to be formed. A mass of material 1012 forforming the waveguide is deposited on the mold 1202.

With reference to FIG. 12B, the molds 1200, 1202 are brought together tocompress the material 1012 (FIG. 12A). The compressed material may besubjected to a curing process (e.g., exposure to UV light) to hardenthat material to form the waveguide 1010. As illustrated, the negativepattern 1250 defines the patterned structure 1050, which may bediffractive optical elements. It will be appreciated that additionalnegative patterns may be provided on the mold 1202 to form an additionalstructure, including diffractive optical elements, as desired.

With reference to FIG. 12C, the molds 1200, 1202 are moved apartrelative to one another. The waveguide 1010 is released from the molds,thereby forming the waveguide 1000.

With reference to FIGS. 12A-12C, it will be appreciated that, in someother embodiments, the raised features 1230 are omitted, such that theresulting waveguide 1000 does not include the indentations 1030.Instead, in some embodiments, the spacers of underlying waveguidessimply rests on the bottom major surface of the overlying waveguides.

As discussed herein, the spacers 1020 are preferably formed at locationsaway from the path of propagation of light between incoupling andoutcoupling optical elements of a waveguide. FIGS. 13A-13B illustrateexamples of top-down plan views of waveguides comprising spacers. Asshown in FIG. 13A, the spacers 1020 are preferably positioned along theperiphery of the waveguide 1000. It will be appreciated that the spacers1020 may thus surround an area in which diffractive optical elements,such as incoupling and outcoupling optical elements, are disposed.

In some embodiments, with reference to FIG. 13B, the spacers 1020 may beelongated along the same axis 1042 as the surface relief features 1040.In such embodiments, the spacers 1020 may include spacers having arelatively long expanse along the axis 1042, and a plurality of otherspacers 1020′ having relatively shorter expenses. For example, theseother spacers 1020′ may be spaced-apart and arrayed in groups 1024, withthe groups of spacers spaced-apart along an axis that crosses the axis1042. Advantageously, having the spacers 1020, 1020′ elongated along thesame axis 1042 as the surface relief features 1040 can facilitateconsistent manufacturing of the spacers and the surface relief features.For example, in some embodiments, the spacers and the surface relieffeatures may be formed by imprinting using a mold that is subsequentlyremoved by peeling the mold and the waveguide away from one another. Itwill be appreciated that this peeling away may be performed along theaxis 1042 and that spacers or surface relief features elongated along adifferent axis may face an increased likelihood of breakage ordeformation upon removal of the mold.

With reference now to FIG. 14, an example of a waveguide comprisingspacers 1020 and indentations 1030 of varying dimensions is illustrated.It will be appreciated that some spacers 1020 may be wider than others.The widths of the spacers 1020 may vary depending upon their location onthe waveguide 1000. For example, spacers 1020 at locations less likelyto interact with light may be wider than spacers 1020 at locations inwhich the spacers 1020 are more likely to receive light andunintentionally leak that light into neighboring waveguides.

With continued reference to FIG. 14, in some embodiments, multipleside-by-side spacers 1020 and/or multiple side-by-side indentations 1030may be provided in place of a single one of the spacers 1020 andindentations 1030 illustrated in FIG. 10A. For example, as illustrated,two side-by-side spacers 1020 and two corresponding side-by-sideindentations 1030 may be provided in place of a single one of thespacers 1020 and 1030 of FIG. 10A. In some embodiments, the side-by-sidespacers and indentations may have different widths. In some embodiments,spacers may be provided on both top and bottom major surfaces of thewaveguide 1000. In such embodiments, the spacers and the indentationsmay interlock when forming a stack, thereby advantageously increasingthe stability and mechanical strength of a stack of waveguides formedusing these waveguides. In some embodiments, individual ones of thespacers 1020 may include multiple tiers which decrease in width withdistance from a major surface of the waveguide.

In some embodiments, the waveguide 1000 may be a hybrid waveguide formedby multiple layers of different materials. For example, the hybridwaveguide may include a core layer and at least one auxiliary layer.Preferably, the core layer is formed of a highly transparent materialand the auxiliary layer is formed of a thinner layer of material, inwhich surface relief structures, such as diffractive optical elements,are provided. In some embodiments, the material forming the core layeris a highly transparent polymer, e.g., having a transparency relaytransmission of greater than 85%, greater than 90%, or greater than 96%in the visible light spectrum across the thickness of the core layer.The material may be a flowable material (e.g., a flowable polymer) whichmay be flowed onto a surface and subsequently hardened, e.g., by curing.The auxiliary layer may be thinner than the core layer and is preferablyformed of a different material than the core layer. In some embodiments,the auxiliary layer is formed of a polymer (e.g., an organic polymer),an inorganic material, a hybrid organic/inorganic material, orcombinations thereof. In some embodiments, for a given thickness, theauxiliary layer may have lower transparency in the visible spectrumand/or have lower homogeneity (in composition and/or optical propertiessuch as transparency) than the core layer. However, this lowertransparency and/or lower homogeneity may be ameliorated by the relativethinness of the auxiliary layer in comparison to the core layer.

Preferably, the core layer is formed of a material with a highrefractive index, which may provide an advantageously large field ofview for display devices utilizing the core layer in the waveguide. Insome embodiments, the material forming the core layer may have arefractive index of about 1.65 or more, about 1.70 or more, or about1.80 or more. In addition, the auxiliary layer may be formed of amaterial with a different refractive index than the core layer. It willbe appreciated that differences in refractive indices at an interfacecomprising nanophotonic structures can facilitate the ability ofdiffractive optical elements in that layer to redirect light. In someembodiments, the material forming the auxiliary layer has a refractiveindex that differs from the refractive index of the material forming thecore layer by about 0.05 or more, about 0.1 or more, or about 0.2 ormore. In some embodiments, waveguide may include an additional auxiliarylayer in which indentations and/or additional surface relief features(e.g., diffractive optical elements) are formed. Additional detailsregarding hybrid waveguides are disclosed in U.S. Application No.62/651,507 filed on Apr. 2, 2018, entitled HYBRID POLYMER WAVEGUIDE ANDMETHODS FOR MAKING THE SAME, the entirety of which is incorporated byreference herein.

In some embodiments, the core and auxiliary layers may be formed usingflowable materials, without vapor deposition. The core layer may beformed of relatively high refractive index materials as described abovefor the waveguide 1000, and the auxiliary layer may be formed of a lowerrefractive index material. Examples of lower refractive index materials(e.g., having a refractive index lower than 1.65) include organicpolymer materials, low refractive index resins, sol-gel based hybridpolymers (e.g., TiO₂, ZrO₂, and ITO sol-gel materials), polymers dopedwith nanoparticles (such as TiO₂, ZrO₂), and active materials (e.g.,polymers doped with quantum dots). Examples of low refractive indexorganic polymer materials include those commercially available fromSigma-Aldrich of St. Louis, Mo., USA, such as the polymer material soldunder the names CPS 1040 UV, CPS1040 UV-A, CPS1030, CPS 1020UV, CPS1040UV-VIS, CPS 1030 UV-VIS, and CPS 1020 UV-VIS. Examples of lowrefractive index resins include those commercially available from Miwonof the Nagase Group, Osaka, Japan.

In some embodiments, patterns (e.g., patterns defining diffractiveoptical elements) may be formed during the formation of the core and/orauxiliary layer without separate patterning and etch processes. Forexample, the patterns may be formed by imprinting and subsequentlyhardening or curing of the imprinted material.

FIGS. 15A-15G illustrate a method of forming a hybrid waveguide with acore layer and overlying and underlying auxiliary layers. With referenceto FIG. 15A, a pair of molds 1201, 1202 is provided, with the mold 1202comprising a pattern of raised features 1250 for forming surface relieffeatures in the auxiliary layer to be formed. A mass of material 1300for forming the auxiliary layer is subsequently deposited on the mold1202. With reference to FIG. 15B, the molds 1201, 1202 are moved closertogether to compress the mass of material 1300 (FIG. 16A). Thecompressed material 1300 may be subjected to a curing process (e.g., byexposure to UV light), which hardens those materials to form a solidauxiliary layer 1031. With reference to FIG. 15C, the molds 1201 isseparated from the auxiliary layer 1031 and a mass of core layermaterial 1310 is deposited on the auxiliary layer 1031. With referenceto FIG. 15D, the molds 1201, 1202 are moved closer together to compressthe mass of material 1310, thereby forming the core layer 1010. Thecompressed material may be subjected to a curing process (e.g., exposureto UV light), which hardens that material to form a solid core layer1010. With reference to FIG. 15E, the mold 1201 is separated from thecore layer 1010 and replaced with the mold 1200. The mold 1200 includesa pattern of protrusions 1240 for defining surface relief features in anadditional auxiliary layer. An additional mass of material 1320 forforming the additional auxiliary layer is deposited on the core layer1010. With reference to FIG. 15F, the molds 1200, 1202 are moved closertogether to compress the mass of material 1320 (FIG. 16E) to define theauxiliary layer 1021. It will be appreciated that the pattern offeatures 1240 imprints the desired surface relief features 1040 in theauxiliary layer 1021. The compressed material forming the auxiliarylayer 1021 may be subjected to a curing process to harden that materialto form the solid auxiliary layer 1020. With reference to FIG. 15G, themolds 1200, 1202 are moved apart and a hybrid waveguide comprising thecore layer 1010 and the auxiliary layers 1031, 1021 is released from themolds.

In some other embodiments, the core and auxiliary layers may be formedof different flowable materials which are immiscible. These materialsmay be deposited one on top of the other and then subsequentlycompressed and hardened. Further details regarding such a process arefound in U.S. Application No. 62/651,507 filed on Apr. 2, 2018, entitledHYBRID POLYMER WAVEGUIDE AND METHODS FOR MAKING THE SAME.

With reference again to FIGS. 12A-12C and 15A-15G, it will beappreciated that the molds 1200, 1201, 1202 may be patterned withnegatives of the spacers and the surface relief features to be formed.In addition, the molds preferably have sufficient rigidity to imprintfeatures into the various flowable materials used to form thewaveguides. Examples of materials for forming the molds include glass,fused silica, quartz, silicon, and metals.

Negatives the spacers may be defined in these materials using variousprocesses, depending upon whether the spacers have vertical or inclinedsidewalls. For spacers with vertical sidewalls, the spacers, as seen ina top-down view, may first be patterned using lithography, e.g. bypatterning a photoresist deposited on the material to be patterned, andthen etched through the patterned photoresist using a directional etch.Examples of directional etches include dry etches such as RIE, ICP,sputter etching. In some other embodiments, a wet etch (e.g., comprisingHF) may be utilized.

For spacers with inclined sidewalls, the negatives of the spacers may beformed using gray-scale lithography to pattern a three-dimensional shapein a resist layer as a mask, and the geometries of that shape aretransferred into the underlying substrate (the mold material) by one ormore dry etch techniques such as RIE, ICP, and sputter etching, or bywet etching. For silicon substrates, the inclined sidewall surfaces mayalso be fabricated using wet chemical etching. In some embodiments, thetop-down view shapes/geometries may first be patterned in a resist layerusing lithography, and then the substrate (the mold) is etched firstusing a dry etch, and then a wet etch. In the case of a silicon mold,the silicon wet etch may include KOH and TMAH.

Example Waveguide Structures for Reducing Propagation of UnutilizedLight Out of the Waveguide

As discussed herein, not all of the light propagating through awaveguide may be out-coupled as the light makes a single pass across thewaveguide. The light which remains after propagating across thewaveguide to an edge of the waveguide may be referred to as unutilizedlight. As also discussed herein, optical artifacts may result if thisunutilized light were to propagate out of the waveguide. Variousembodiments disclosed herein provide edge treatments which mitigate therecirculation of light within the waveguide after it contacts an edge orthe area near an image, thereby reducing the likelihood that unutilizedlight will propagate out of the waveguide.

In some embodiments, the edge treatment may comprise light absorbingmaterials covering one or more images of a waveguide. Referring now toFIG. 16, an example of a waveguide 1602 having edges covered with lightabsorbing materials illustrated. The waveguide 1602 has a top majorsurface 1601 and bottom major surface 1603 and an edge 1605. The edge1605 is covered with light absorbing material 1604. The light absorbingmaterial 1604 may, in some embodiments, be a layer of light absorbingmaterial applied on the edge of waveguide 1602 and may absorb unutilizedlight beams, as such light beams 1606 and 1608, that are travellingtowards the edges. The unutilized light beams may include light beamsthat are not outcoupled from the waveguide 1602 to a viewer. Theunutilized light beams may reflect off of the edge 1605 of the waveguide1602, propagate back through the waveguide 1602, and then be outcoupledfrom waveguide 1602 (e.g., via outcoupling elements such as out-couplingoptical elements 800, 810, 820 of FIG. 9B) as ghost images and/or straylight which decrease image quality.

With continued reference to FIG. 16, without the light absorbingmaterial 1604, light beams, such as light beam 1608, that strike theedge of waveguide 1602 with relatively large incident angles may reflectback from the edge and reduce the contrast (e.g. by impinging on the topmajor surface 1601 of the waveguide at an angle such that the lightescapes total internal reflection to propagate out of the waveguide1602). Similarly, light beams having relatively small incident angles,such as light beam 1606, that exit out of the waveguide 1602 may stillhave some portion, such as reflection 1607, reflecting back into thewaveguide due, as examples, to a difference in refractive index(Δn=n_(waveside)−n_(ink)) between the waveguide 1602 forming aninterface with the edge of the waveguide.

Without being limited by theory, it has been found that the refractiveindex (n) and the extinction coefficient (k) of an edge-applied lightabsorbing material, such as material 1604 applied to waveguide 1602,influence how well the by the absorbing material extracts and absorbslight from a waveguide. Simulations were performed for light absorptionversus reflection for light beams striking an edge-applied lightabsorbing material, as a function of the extinction coefficient (k) ofthe light absorbing material and as a function of the angle of incidence(e.g., measured relative to a vector that is normal to the plane of thewaveguide edge, shown in FIG. 16 as ⊕, where light beam 1606 has alarger incident angle than light beam 1608). The simulations wereperformed for absorption of s-polarized light (e.g., transverse-electricTE polarized light) and absorption of p-polarized light (e.g.,transverse-magnetic TM polarized light), and averages were obtained todetermine an absorption average for s-polarized light and p-polarizedlight. The simulations assumed a waveguide having an index of refractionof 1.73. Some of the simulations assumed light absorbing material havingan index of refraction of 1.55, while some of the simulations assumedlight absorbing material having an index of refraction of 1.65. Thesimulation results indicated that light beams with higher incidentangles (e.g., light beams that strike the light absorbing material 1604relatively directly instead of in a glancing manner) are not fullyabsorbed and may be reflected. In particular, as incident anglesincrease beyond about 65 degrees, absorption drops off and the lightstarts to reflect off of the edge 1605 (e.g., due to the difference inindex of refraction between waveguide 1602 and the light absorbingmaterial 1604). The simulation results also indicate that increasing theextinction coefficient, k, of the light absorbing material 1604 booststhe absorption of higher-incident-angle light beams, but the boost isrelatively limited (e.g., absorption at k=0.05 is only about 50% higherthan absorption at k=0.005, all other factors being constant).

Again, without being limited by theory, the simulation results indicatethat the light absorbing material having an index of refraction of 1.65significantly outperformed the light absorbing material having an indexof refraction of 1.55. This is believed to be due to the lowerdifference in index of refraction between the waveguide and the lightabsorbing material. Thus, the simulation results illustrate that, toimprove light absorption by the light absorbing material 1604, it ishelpful to reduce the difference in indices of refraction of thewaveguide 1602 and the light absorbing material 1604 and also helpful,but to a lesser extent, to utilize a light absorbing material 1604 witha high extinction coefficient (k). In some embodiments, the differencein indices of refraction of the waveguide 1602 and the light absorbingmaterial 1604 is 0.2 or less. In addition, in some embodiments, thelight absorbing material 1604 has an extinction coefficient (k) of atleast 0.02.

It will be appreciated that the above discussion relates to a singleinteraction of light beams and with the edge 1605 and the lightabsorbing material 1604. To further improve absorption of light beamsinto the light absorbing material, the coverage area of the lightabsorbing material may be increased as illustrated in FIGS. 17 and 18,in which the light absorbing material extends over a larger portion ofthe waveguide.

FIGS. 17-18 illustrate an example of a waveguide having light absorbingmaterial extending on portions of top and bottom major surfaces 1801,1803 of the waveguide 1802. As illustrated, light absorbing material1804 that covers at least one edge 1805 of the waveguide 1802 and alsoextends over edge-adjacent portions of the top and bottom major surfaces1801, 1803 of the waveguide. In particular, the light absorbing material1804 may be formed on portions of the waveguide 1802 that extend for aparticular distance, illustrated as length of blackening 1806, away fromthe edge 1805 of the waveguide 1802.

As shown in FIG. 18, extending the light absorbing material 1804 overthe length 1806 can create multiple interactions between propagatinglight beams and the light absorbing material 1804, thus increasingabsorption of the unutilized light beams. In particular, FIG. 18illustrates how a particular light beam 1808 propagating withinwaveguide 1802 via total internal reflection (TIR) may interact withlight absorbing material 1804 at point 1810 a and also at point 1810 b.

In general, the length 1806 needed to ensure that propagating lightinteracts with the light absorbing material 1804 multiple times may varydepending on the difference in index of refraction between the waveguide1802 and adjacent materials (which may be air), the thickness of thewaveguide 1802, the wavelengths of light passing through the waveguide1802, a grating design (e.g., a design of outcoupling elements such asout-coupling optical elements 800, 810, 820 of FIG. 9B), the field ofview of waveguide 1802, among other possible factors. FIG. 18illustrates a particular example of blue light propagating via TIRinside glass having an index of refraction of 1.8 with air as anadjacent material, where a length of blackening of at leastapproximately 1.87 mm of black ink (with n=1.73) is sufficient to ensuremultiple interactions. In some embodiments, the length 1806 may extendapproximately 2 mm, approximately 5 mm, or between approximately 2-5 mmfrom the waveguide edge in order to effectively absorb a large portionof the propagating light that reaches the edge of the waveguide.

It has been determined that the thickness of an edge-applied lightabsorbing material, such as material 1604 applied to waveguide 1602 andmaterial 1804 applied to waveguide 1802, influences well the materialextracts and absorbs light from a waveguide. Studies of absorption oflight by a light absorbing material such as black ink were performed formaterials of three different indices of refraction (n=1.55, n=1.65, andn=1.73). Various simulations showed potential thicknesses of materialthat may be utilized to achieve a desired level of absorption (e.g., acertain minimum percentage of absorption, which may be at least 95%absorption) as a function of the incident angle and as the extinctioncoefficient was varied from approximately 7×10⁻³ to approximately10×10⁻³. In general, larger thicknesses of material achieved a desiredlevel of absorption when the incident angle is low (e.g., when lightstrikes the material relatively perpendicularly) as compared to when theincident angle is high (e.g., when light strikes the material in aglancing manner). Additionally, larger thicknesses of material achievedthe desired level of absorption when the extinction coefficient islower, however, the absorption rates were less dependent on theextinction coefficient than on the incident angle. The simulationsfurther indicated that a material thickness of approximately 20 μm maybe utilized to achieve advantageously high levels of absorption for arange of simulated incident angles (e.g., approximately 20 degrees fromperpendicular to approximately 70 degrees from perpendicular) and adesired range of simulated extinction coefficients (e.g., extinctioncoefficients from approximately 7×10⁻³ to approximately 10×10⁻³). Insome embodiments, the light absorbing material has a thickness of 20 μmor more.

Any suitable material may be used as edge-applied light absorbing orblackening material (e.g., material 1604 applied to waveguide 1602 andmaterial 1804 applied to waveguide 1802). As examples, edge-appliedlight absorbing or blackening materials may include thin film materialssuch as fullerene, graphene, amorphous silicon, germanium, etc., whichmay be deposited on a waveguide surface by physical or chemical vapordeposition or via other suitable processing deposition processes; blackinks including low viscosity black ink such as black inkjet availablefrom Nazdar of Shawnee, Kans., which may be applied by inkjet printingor other suitable methods; and light absorbing additives dispersed ordissolved in a polymer (e.g., an UV curable polymer resin), such ascarbon black, carbon nanopowder, carbon nanotubes, metallicnanoparticles, color dyes, pigments, phosphors, etc.

Simulation results of the reflection rates of various different lightabsorbing materials are shown in graph 2000 of FIG. 19 and graph 2050 ofFIG. 20. The simulations of FIGS. 19 and 20, involve a singleinteraction of a light beam with the light absorbing materials.

The different light absorbing materials simulated for FIG. 19 include aplot 2002 for black ink and plots 2004, 2006, 2008, 2010, 2012, 2014 forvarying concentrations of carbon nanopowder dispersed or dissolved in aresin. As shown by plot 2002 in FIG. 19, black ink has a low reflectance(e.g., a reflectance below 10% and thus an absorption rate of at least90%) for incident angles below about 55 degrees. However, thereflectance of the black ink substantially increases above 55 degrees.As shown by plots 2004, 2006, 2008, 2010, 2012, and 2014, increasing theconcentration of carbon in the light absorbing materials tends todecrease the reflectance, and thus increase the absorption rate, of thelight absorbing materials. However, once a certain concentration ofcarbon is reached, the performance of the light absorbing materialslevels off and further increases in carbon concentration to not furtherdecrease reflectance. In particular, FIG. 19 illustrates thatconcentrations of approximately 1.56% carbon (plot 2010), 6.25% carbon(plot 2012), and 25% carbon (plot 2014) have relatively similarreflection and absorption performance across the simulated incidentangles.

The different light absorbing materials simulated for FIG. 20 include aplot 2052 for etercure 6948.8B.28 (e.g., a blue dye), plot 2054 fororange LPB (e.g., an orange dye), plot 2056 for red LPB (e.g., a reddye), and plot 2058 for RS1813 jet black (e.g., a black dye). As shownin FIG. 20, the orange and red dyes are able to maintain reflectionrates below 10% over the entire range of simulated incident angles, asseen in plots 2056 and 2058. In contrast, the blue dye has a reflectionrate below 10% only for the simulated incident angles that are belowapproximately 53 degrees, as seen in plot 2054, and the black dye has areflection rate below 10% only for the simulated incident angles thatare below approximately 63 degrees, as seen in plot 2052.

Another technique for absorption and/or preventing reflection of lightbeams at the edge of a waveguide is roughening of a waveguide edge, asshown in FIG. 21. A waveguide 2100 may be roughened to provide an edge2105 with a rough texture. In some embodiments, edge 2105 is coveredwith light absorbing material 2104. The waveguide 2102 may be roughedalong its edge and also over top and bottom major surfaces 2101, 2103extending away from the edge over a length of roughening 2110, which maybe less than a length of blackening 2112 over which the light absorbingmaterial 2104 is applied. In some embodiments, the length of roughening2110 may be between 2 mm and 5 mm from the edge of waveguide 2100 andthe length of blackening 2112 may extend from the waveguide edge tobetween 2 mm and 5 mm beyond the roughened area. Roughening thewaveguide 2100 in this manner may help to diffuse propagating light, asshown by the scattering of light beam 2106 when it hits the roughenedarea of the waveguide 2100 with applied light absorbing material 2104.Without being limited by theory, the diffusion of light beams such aslight beam 2106 may increase interaction between the light beam and thelight absorbing material 2104, leading to increased rates of absorptionoverall.

The edges and adjacent surfaces of waveguide 2100 (extending in from thewaveguide edge over length of roughing 2110) may be roughened by sandingthe waveguides, by forming the waveguides with molds having a roughtexture, or by other methods. Different grit sizes may be used to insanding waveguides to different roughness. As examples, grit havingP150-100 μm particles or grit having P2500-8.4 μm particles may be usedin sanding waveguides to a desired roughness. Waveguides may be formed,sanded, or otherwise processed to have a surface roughness (Sa) of atleast 1, in certain embodiments. In some embodiments, the surfaceroughness (Sa) is in a range of 1 to 100. In some embodiments, thewaveguide may be roughened radially, such that less light is scatteredback towards an active eyepiece area (e.g., away from the edge).

Additional techniques for improving the absorption of light beams at theedge of a waveguide include forming diffractive gratings, as shown inFIG. 22A, or light-trapping structures, as shown in FIGS. 22B and 22C,along the edges of a waveguide.

FIG. 22A illustrates a waveguide 2200 a with an edge 2205 covered withlight absorbing material 2204, the light absorbing material 2204extending over an area of blackening 2212 on the top and bottom majorsurfaces 2201, 2203, where the waveguide 2202 a includes out-couplingoptical elements 2220 over an area of gratings 2210 a extending on thetop and bottom major surfaces 2201, 2203 of the waveguide 2202 a. Insome embodiments, the out-coupling optical elements 2220 are diffractivegratings. In some embodiments, waveguide 2202 a may have out-couplingoptical elements on its edge in addition or instead of having suchgratings on the top and bottom major surfaces 2201, 2203 adjacent to theedge. In some embodiments, the light absorbing material 2204 may beomitted.

The out-coupling optical elements 2220 may, as an example, beout-coupling diffractive gratings that are configured to out-couplelight propagating in waveguide 2202 a such as light beams 2206 and 2208into the light absorbing material 2204, where the light is absorbed. Asan example, the area of gratings 2210 a may extend out between 2 mm and5 mm from the edge of waveguide 2202 a (e.g., which may ensure that anylight beams propagating in the waveguide interact with the gratings) andthe area of blackening 2212 may further extend out between 2 mm and 5 mmfrom the area of gratings 2210 a (e.g., which may facilitate theabsorption of light, scattered by the gratings, by the light absorbingmaterial 2204). The design of the gratings 2220 may vary depending onthe indices of refraction of the waveguide 2202 a and light absorbingmaterials 2204, the wavelength(s) of light propagating through thewaveguide 2202 a, and among other possible factors. In some embodiments,diffractive gratings 2220 may be formed in waveguide 2202 a bypatterning a mold in which the waveguide 2202 a is formed. Diffractivegratings 2200 may, in some embodiments, be formed as part of and/orusing the same fabrication techniques used in forming other diffractiveelements disclosed herein, such as the out-coupling optical elements800, 810, and 820 of FIG. 9B, and integral spacers, as disclosed herein.

FIG. 22B illustrates a waveguide 2202 a with an edge 2205 covered withlight absorbing material 2204 which also extends over an area ofblackening 2212 on the top and bottom major surfaces 2201, 2203, wherethe top and bottom major surfaces 2201, 2203 of the waveguide 2202 ainclude light trapping structures 2230 a and/or 2230 b over a lighttrapping area 2210 b extending from the edge 2205. In some embodiments,waveguide 2202 b may have light trapping structures on its edge inaddition or instead of having such structures on the top and bottommajor surfaces 2201, 2203 adjacent to the edge. In some embodiments, thelight absorbing material 2204 may be omitted. The light trappingstructures 2230 a and 2230 b may, as an example, be microstructures. Asshown in FIG. 22C, a simulated light beam 2232 that enters the edgeregion of waveguide 2202 b does not escape the edge region withoutmultiple interactions, due to the shape and size of the light trappingstructures 2230 a and 2230 b. As illustrated, during one of theseinteractions, light may escape the waveguide and propagate into thelight absorbing material 2204 (FIG. 22B) light absorbing material 2204.Without being limited by theory, the light trapping structures 2230 aand 2230 b may advantageously increase the absorption of light.

In some embodiments, the area of light trapping 2210 b may be between 2mm and 5 mm from the edge of waveguide 2202 b (e.g., which may increasethe likelihood that light beams propagating in the waveguide interactwith the light trapping structures) and the area of blackening 2212 mayextend between 2 mm and 5 mm from the area of light trapping 2210 b(e.g., which may increase the likelihood that that any light scatteredby the light trapping structures is absorbed by the light absorbingmaterial 2204). In some embodiments, light trapping structures such asstructures 2230 a and 2230 b may be formed in waveguide 2202 b bypatterning a mold in which the waveguide 2202 b is formed. Lighttrapping structures 2230 a and 2230 b may, in some embodiments, beformed as part of and/or using the same fabrication techniques used informing diffractive elements disclosed herein, such as the out-couplingoptical elements 800, 810, and 820 of FIG. 9B and integral spacers, asdisclosed herein.

The design of the light trapping structures 2230 a and 2230 b may varydepending on the indices of refraction of the waveguide 2202 b and lightabsorbing materials 2204, the wavelength(s) of light propagating throughthe waveguide 2202 b, and among other factors. In some embodiments, thewidth and heights of the light trapping structures 2230 a and 2230 branges from 0.5 μm to 100 μm. As examples, the width and heights of thelight trapping structures 2230 a and 2230 b may approximately 0.5 μm,approximately 1.0 μm, approximately 2.0 μm, approximately 4.0 μm,approximately 10.0 μm, approximately 20.0 μm, approximately 50 μm,approximately 75 μm, or approximately 100 μm, wherein approximately isunderstood to be within 0.4 μm.

It will be appreciated that any of the strategies for improving lightabsorption at the edge of a waveguide may be combined together. As anexample, a waveguide may include light absorbing material on an edge andalso extending inwardly from the waveguide edge (as disclosed in FIGS.17 and 18), having a sufficient thickness for desired levels of lightabsorption, being made from materials as disclosed at least in FIGS. 19and 20, and having any of a roughening of the waveguide surface (asdisclosed in FIG. 21), diffractive gratings (as disclosed in FIG. 22A),and/or light trapping structures (as disclosed in FIGS. 22B and 22C).

FIG. 23 illustrates edges 2404 a, 2404 b of a waveguide 2400 that havehigher levels of unutilized light. The strategies disclosed herein forimproving light absorption at the edge of a waveguide may be applied toall of the edges of a waveguide or, in some embodiments, may be appliedonly to the areas of the waveguide expected to have higher levels ofunutilized light relative to other areas of the waveguide. For example,the edges 2404 a, 2404 b of FIG. 23 may be considered to have highlevels of unutilized light. The areas with the high levels of unutilizedlight may be the areas of the waveguide in which relatively high amountsof light reach the waveguide edge without being out-coupled. Suchunutilized light, if not absorbed at the edge, could potentially reflectback into an active display region and create undesirable ghost imagesor stray light, thus lowering image quality. In some embodiments, thearea of waveguide 2400 with the high levels of unutilized light includeedges 2404 a adjacent to the in-coupling optical elements 700, 710, 720.The edges 2404 a are on a side of the in-coupling optical elements 700,710, 720 opposite to the direction in which light is directed by thein-coupling optical elements 700, 710, 720 for eventual out-coupling.Another area with high levels of unutilized light includes the edges2404 b adjacent to the out-coupling optical elements 800, 810, 820.Light in this area includes light that has propagated across theout-coupling optical elements 800, 810, 820 without being out-coupled.It will be appreciated that light incident on these edges is unutilizedsince the light was not out-coupled after passing through these opticalelements intended for out-coupling. In contrast, edges adjacent to thelight distributing elements 730, 740, 750 may have relatively low levelsof unutilized light and thus may not benefit as much from the lightabsorption strategies described herein.

As noted herein, it will be appreciated that the various waveguides1602, 1802, 2102, 2202 a, and 2202 b of FIGS. 16-18 and 21-23 mayinclude one or more integral spacers and/or indentations foraccommodating a spacer. In addition, in some embodiments, the waveguides1602, 1802, 2102, 2202 a, and 2202 b may be part of a stack ofwaveguides, each of which may include an integral spacer and indentationfor accommodating an underlying spacer from an underlying waveguide,which also includes an integral spacer.

FIG. 24 illustrates a stack of waveguides with integral spacers. Theillustrated individual waveguides may be any of the waveguides 1602,1802, 2102, 2202 a, 2202 b which are also illustrated in FIGS. 16-18 and21-23. It will be appreciated that only the portions of the waveguides1602, 1802, 2102, 2202 a, 2202 b having an integral spacer 1020 and/orindentation 1030 are shown in this figure for clarity. The remainder ofthe waveguides 1602, 1802, 2102, 2202 a, and 2202 b are shown in thecorresponding one of FIGS. 16-18 and 21-23, and may include various edgetreatments (e.g., light absorbing material, rough textures, out-couplingoptical elements, light-trapping microstructures) as disclosed herein.In some embodiments, the waveguides 1602, 1802, 2102, 2202 a, 2202 beach have one or more integral spacers 1020 configured to provideseparation between that waveguide and an immediately neighboring,overlying waveguide. Thus, as illustrated, the waveguides 1602, 1802,2102, 2202 a, 2202 b with integral spacers may form a waveguide stack(e.g., corresponding to the waveguide stack 660 of FIGS. 9A-9C). In someembodiments, each of the waveguides 1602, 1802, 2102, 2202 a, 2202 b ofthe waveguide stack may be similar (e.g., have similar edge treatments).In some other embodiments, the waveguides forming the waveguide stackmay have different edge treatments (e.g., different ones of thewaveguides 1602, 1802, 2102, 2202 a, 2202 b from FIGS. 16-18 and 21-23may be utilized in different positions within the waveguide stack).

It will be appreciated that the integral spacers 1020 and/orindentations 1030 of the waveguides 1602, 1802, 2102, 2202 a, and 2202 bmay be formed and have shapes and orientations as described aboveregarding FIGS. 10A-15G. For example, in some embodiments, thewaveguides 1602, 1802, 2102, 2202 a, 2202 b and integral spacers 1020may be formed of a polymer material that may be molded (e.g., using animprint mold) to define the integral spacers 1020. In addition, asdiscussed herein, the mold may include relief features for defining oneor more of in-coupling optical elements, out-coupling optical elements,rough surface textures on and adjacent an edge 2105 (FIG. 21),out-coupling optical elements 2220 (FIG. 22A), and light trappingstructures 2230 a and/or 2230 b (FIGS. 22B and 22C).

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than restrictive sense.

Indeed, it will be appreciated that the systems and methods of thedisclosure each have several innovative aspects, no single one of whichis solely responsible or required for the desirable attributes disclosedherein. The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure.

Certain features that are described in this specification in the contextof separate embodiments also may be implemented in combination in asingle embodiment. Conversely, various features that are described inthe context of a single embodiment also may be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination. No single feature orgroup of features is necessary or indispensable to each and everyembodiment.

It will be appreciated that conditional language used herein, such as,among others, “can,” “could,” “might,” “may,” “e.g.,” and the like,unless specifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/or stepsare included or are to be performed in any particular embodiment. Theterms “comprising,” “including,” “having,” and the like are synonymousand are used inclusively, in an open-ended fashion, and do not excludeadditional elements, features, acts, operations, and so forth. Also, theterm “or” is used in its inclusive sense (and not in its exclusivesense) so that when used, for example, to connect a list of elements,the term “or” means one, some, or all of the elements in the list. Inaddition, the articles “a,” “an,” and “the” as used in this applicationand the appended claims are to be construed to mean “one or more” or “atleast one” unless specified otherwise. Similarly, while operations maybe depicted in the drawings in a particular order, it is to berecognized that such operations need not be performed in the particularorder shown or in sequential order, or that all illustrated operationsbe performed, to achieve desirable results. Further, the drawings mayschematically depict one more example processes in the form of aflowchart. However, other operations that are not depicted may beincorporated in the example methods and processes that are schematicallyillustrated. For example, one or more additional operations may beperformed before, after, simultaneously, or between any of theillustrated operations. Additionally, the operations may be rearrangedor reordered in other embodiments. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system components in the embodiments describedabove should not be understood as requiring such separation in allembodiments, and it should be understood that the described programcomponents and systems may generally be integrated together in a singlesoftware product or packaged into multiple software products.Additionally, other embodiments are within the scope of the followingclaims. In some cases, the actions recited in the claims may beperformed in a different order and still achieve desirable results.

Accordingly, the claims are not intended to be limited to theembodiments shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

1.-54. (canceled)
 55. A display system comprising: an eyepiececomprising a stack of waveguides, wherein at least one of the waveguidescomprises: an optically transmissive body comprising: diffractiveoptical elements comprising a plurality of protrusions and interveningrecesses on a major surface of the optically transmissive body; and aplurality of spacers integral with the optically transmissive body,wherein the spacers extend to a height greater than a height of thediffractive optical elements, wherein the overlying waveguide isdisposed on the spacers, and wherein the spacers separate the opticallytransmissive body from the overlying waveguide by a gap.
 56. The displaysystem of claim 55, wherein the overlying waveguide comprisesindentations accommodating the spacers in the indentations.
 57. Thedisplay system of claim 56, wherein each of the waveguides comprisesspacers and indentations, wherein the indentations accommodate spacersof underlying waveguides.
 58. The display system of claim 56, whereinthe spacers comprise multiple tiers having progressively narrower widthswith increasing height, wherein the indentations comprise openingshaving multiple tiers with narrower widths as height increases.
 59. Thedisplay system of claim 55, wherein sizes of the spacers vary across themajor surface.
 60. The display system of claim 59, wherein the spacersare arranged in groups, wherein neighboring spacers of a group havedifferent sizes.
 61. The display system of claim 55, wherein, as seen ina top-down view, the spacers comprise one or more shapes selected fromthe group consisting of rectangular prism, rectangular pyramid,triangular prism, triangular pyramid, cylinder, and cone.
 62. Thedisplay system of claim 55, further comprising an adhesive attaching thespacers to the overlying waveguide.
 63. The display system of claim 62,wherein the adhesive is configured to absorb light.
 64. The displaysystem of claim 55, further comprising a pattern of light scatteringfeatures on tops of the spacers.
 65. The display system of claim 55,wherein the overlying waveguide comprises diffractive optical elementsconfigured to redirect light of different wavelengths than thediffractive optical elements of the at least one of the waveguides. 66.The display system of claim 55, wherein the gap is an air gap.
 67. Adisplay system comprising: an eyepiece comprising a waveguidecomprising: an optically transmissive body comprising: diffractiveoptical elements comprising a plurality of protrusions and interveningrecesses on a major surface of the optically transmissive body; and aplurality of spacers integral with the optically transmissive body,wherein the spacers extend from the major surface to a height greaterthan a height of the diffractive optical elements.
 68. A method formaking an eyepiece, the method comprising: forming a waveguide, whereinforming the waveguide comprises: defining integral diffractive opticalelements and integral spacers on a major surface of the waveguide, wherethe spacers are spaced-apart from the diffractive optical elements andextend to a height above the diffractive optical elements.
 69. Themethod of claim 68, wherein defining integral diffractive opticalelements and integral spacers comprises forming the diffractive opticalelements and the spacers simultaneously.
 70. The method of claim 68,wherein defining integral diffractive optical element and integralspacers comprises patterning light scattering features on tops of thespacers.
 71. The method of claim 68, wherein defining integraldiffractive optical elements and integral spacers comprises: providingupper and lower imprint molds, wherein the imprint molds face oneanother; providing a flowable material on the lower imprint mold;contacting the flowable material with the upper imprint mold; subjectingthe flowable material to a hardening process, wherein the hardenedflowable material forms the waveguide; and removing the upper and lowerimprint molds.
 72. The method of claim 71, wherein the upper imprintmold comprises a pattern of protrusions and indentations, whereincontacting the flowable material with the upper imprint mold transfers acorresponding pattern of protrusions and indentations into the flowablematerial to imprint the diffractive optical elements and spacers in theflowable material.
 73. The method of claim 71, further comprising, aftersubjecting the flowable material to the hardening process: removing theupper imprint mold; depositing another flowable material on the hardenedflowable material; and contacting the other flowable material withanother upper imprint mold, wherein the other upper imprint moldcomprises a pattern of protrusions and indentations, wherein contactingthe flowable material with the upper imprint mold transfers acorresponding pattern of protrusions and indentations into the flowablematerial to imprint the diffractive optical elements and spacers in theflowable material.
 74. The method of claim 71, wherein, as seen in atop-down view, the diffractive optical elements comprise a diffractivegrating comprising a plurality of protrusions elongated along an axis,wherein the spacers are elongated and have a length extending along theaxis.
 75. The method of claim 68, further comprising stacking anotherwaveguide on the spacers, wherein the spacers support the otherwaveguide and define a gap between the waveguide and the otherwaveguide.